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 // SPDX-License-Identifier: GPL-2.0-or-later
 /*
  * Copyright (c) International Business Machines Corp., 2006
  * Copyright (c) Nokia Corporation, 2006, 2007
  *
  * Author: Artem Bityutskiy (Битюцкий Артём)
  */
 
 /*
  * UBI input/output sub-system.
  *
  * This sub-system provides a uniform way to work with all kinds of the
  * underlying MTD devices. It also implements handy functions for reading and
  * writing UBI headers.
  *
  * We are trying to have a paranoid mindset and not to trust to what we read
  * from the flash media in order to be more secure and robust. So this
  * sub-system validates every single header it reads from the flash media.
  *
  * Some words about how the eraseblock headers are stored.
  *
  * The erase counter header is always stored at offset zero. By default, the
  * VID header is stored after the EC header at the closest aligned offset
  * (i.e. aligned to the minimum I/O unit size). Data starts next to the VID
  * header at the closest aligned offset. But this default layout may be
  * changed. For example, for different reasons (e.g., optimization) UBI may be
  * asked to put the VID header at further offset, and even at an unaligned
  * offset. Of course, if the offset of the VID header is unaligned, UBI adds
  * proper padding in front of it. Data offset may also be changed but it has to
  * be aligned.
  *
  * About minimal I/O units. In general, UBI assumes flash device model where
  * there is only one minimal I/O unit size. E.g., in case of NOR flash it is 1,
  * in case of NAND flash it is a NAND page, etc. This is reported by MTD in the
  * @ubi->mtd->writesize field. But as an exception, UBI admits use of another
  * (smaller) minimal I/O unit size for EC and VID headers to make it possible
  * to do different optimizations.
  *
  * This is extremely useful in case of NAND flashes which admit of several
  * write operations to one NAND page. In this case UBI can fit EC and VID
  * headers at one NAND page. Thus, UBI may use "sub-page" size as the minimal
  * I/O unit for the headers (the @ubi->hdrs_min_io_size field). But it still
  * reports NAND page size (@ubi->min_io_size) as a minimal I/O unit for the UBI
  * users.
  *
  * Example: some Samsung NANDs with 2KiB pages allow 4x 512-byte writes, so
  * although the minimal I/O unit is 2K, UBI uses 512 bytes for EC and VID
  * headers.
  *
  * Q: why not just to treat sub-page as a minimal I/O unit of this flash
  * device, e.g., make @ubi->min_io_size = 512 in the example above?
  *
  * A: because when writing a sub-page, MTD still writes a full 2K page but the
  * bytes which are not relevant to the sub-page are 0xFF. So, basically,
  * writing 4x512 sub-pages is 4 times slower than writing one 2KiB NAND page.
  * Thus, we prefer to use sub-pages only for EC and VID headers.
  *
  * As it was noted above, the VID header may start at a non-aligned offset.
  * For example, in case of a 2KiB page NAND flash with a 512 bytes sub-page,
  * the VID header may reside at offset 1984 which is the last 64 bytes of the
  * last sub-page (EC header is always at offset zero). This causes some
  * difficulties when reading and writing VID headers.
  *
  * Suppose we have a 64-byte buffer and we read a VID header at it. We change
  * the data and want to write this VID header out. As we can only write in
  * 512-byte chunks, we have to allocate one more buffer and copy our VID header
  * to offset 448 of this buffer.
  *
  * The I/O sub-system does the following trick in order to avoid this extra
  * copy. It always allocates a @ubi->vid_hdr_alsize bytes buffer for the VID
  * header and returns a pointer to offset @ubi->vid_hdr_shift of this buffer.
  * When the VID header is being written out, it shifts the VID header pointer
  * back and writes the whole sub-page.
  */
 
 #include <linux/crc32.h>
 #include <linux/err.h>
 #include <linux/slab.h>
 #include "ubi.h"
 
 static int self_check_not_bad(const struct ubi_device *ubi, int pnum);
 static int self_check_peb_ec_hdr(const struct ubi_device *ubi, int pnum);
 static int self_check_ec_hdr(const struct ubi_device *ubi, int pnum,
                  const struct ubi_ec_hdr *ec_hdr);
 static int self_check_peb_vid_hdr(const struct ubi_device *ubi, int pnum);
 static int self_check_vid_hdr(const struct ubi_device *ubi, int pnum,
                   const struct ubi_vid_hdr *vid_hdr);
 static int self_check_write(struct ubi_device *ubi, const void *buf, int pnum,
                 int offset, int len);
 
 /**
  * ubi_io_read - read data from a physical eraseblock.
  * @ubi: UBI device description object
  * @buf: buffer where to store the read data
  * @pnum: physical eraseblock number to read from
  * @offset: offset within the physical eraseblock from where to read
  * @len: how many bytes to read
  *
  * This function reads data from offset @offset of physical eraseblock @pnum
  * and stores the read data in the @buf buffer. The following return codes are
  * possible:
  *
  * o %0 if all the requested data were successfully read;
  * o %UBI_IO_BITFLIPS if all the requested data were successfully read, but
  *   correctable bit-flips were detected; this is harmless but may indicate
  *   that this eraseblock may become bad soon (but do not have to);
  * o %-EBADMSG if the MTD subsystem reported about data integrity problems, for
  *   example it can be an ECC error in case of NAND; this most probably means
  *   that the data is corrupted;
  * o %-EIO if some I/O error occurred;
  * o other negative error codes in case of other errors.
  */
 int ubi_io_read(const struct ubi_device *ubi, void *buf, int pnum, int offset,
         int len)
 {
     int err, retries = 0;
     size_t read;
     loff_t addr;
 
     dbg_io("read %d bytes from PEB %d:%d", len, pnum, offset);
 
     ubi_assert(pnum >= 0 && pnum < ubi->peb_count);
     ubi_assert(offset >= 0 && offset + len <= ubi->peb_size);
     ubi_assert(len > 0);
 
     err = self_check_not_bad(ubi, pnum);
     if (err)
         return err;
 
     /*
      * Deliberately corrupt the buffer to improve robustness. Indeed, if we
      * do not do this, the following may happen:
      * 1. The buffer contains data from previous operation, e.g., read from
      *    another PEB previously. The data looks like expected, e.g., if we
      *    just do not read anything and return - the caller would not
      *    notice this. E.g., if we are reading a VID header, the buffer may
      *    contain a valid VID header from another PEB.
      * 2. The driver is buggy and returns us success or -EBADMSG or
      *    -EUCLEAN, but it does not actually put any data to the buffer.
      *
      * This may confuse UBI or upper layers - they may think the buffer
      * contains valid data while in fact it is just old data. This is
      * especially possible because UBI (and UBIFS) relies on CRC, and
      * treats data as correct even in case of ECC errors if the CRC is
      * correct.
      *
      * Try to prevent this situation by changing the first byte of the
      * buffer.
      */
     *((uint8_t *)buf) ^= 0xFF;
 
     addr = (loff_t)pnum * ubi->peb_size + offset;
 retry:
     err = mtd_read(ubi->mtd, addr, len, &read, buf);
     if (err) {
         const char *errstr = mtd_is_eccerr(err) ? " (ECC error)" : "";
 
         if (mtd_is_bitflip(err)) {
             /*
              * -EUCLEAN is reported if there was a bit-flip which
              * was corrected, so this is harmless.
              *
              * We do not report about it here unless debugging is
              * enabled. A corresponding message will be printed
              * later, when it is has been scrubbed.
              */
             ubi_msg(ubi, "fixable bit-flip detected at PEB %d",
                 pnum);
             ubi_assert(len == read);
             return UBI_IO_BITFLIPS;
         }
 
         if (retries++ < UBI_IO_RETRIES) {
             ubi_warn(ubi, "error %d%s while reading %d bytes from PEB %d:%d, read only %zd bytes, retry",
                  err, errstr, len, pnum, offset, read);
             yield();
             goto retry;
         }
 
         ubi_err(ubi, "error %d%s while reading %d bytes from PEB %d:%d, read %zd bytes",
             err, errstr, len, pnum, offset, read);
         dump_stack();
 
         /*
          * The driver should never return -EBADMSG if it failed to read
          * all the requested data. But some buggy drivers might do
          * this, so we change it to -EIO.
          */
         if (read != len && mtd_is_eccerr(err)) {
             ubi_assert(0);
             err = -EIO;
         }
     } else {
         ubi_assert(len == read);
 
         if (ubi_dbg_is_bitflip(ubi)) {
             dbg_gen("bit-flip (emulated)");
             err = UBI_IO_BITFLIPS;
         }
     }
 
     return err;
 }
 
 /**
  * ubi_io_write - write data to a physical eraseblock.
  * @ubi: UBI device description object
  * @buf: buffer with the data to write
  * @pnum: physical eraseblock number to write to
  * @offset: offset within the physical eraseblock where to write
  * @len: how many bytes to write
  *
  * This function writes @len bytes of data from buffer @buf to offset @offset
  * of physical eraseblock @pnum. If all the data were successfully written,
  * zero is returned. If an error occurred, this function returns a negative
  * error code. If %-EIO is returned, the physical eraseblock most probably went
  * bad.
  *
  * Note, in case of an error, it is possible that something was still written
  * to the flash media, but may be some garbage.
  */
 int ubi_io_write(struct ubi_device *ubi, const void *buf, int pnum, int offset,
          int len)
 {
     int err;
     size_t written;
     loff_t addr;
 
     dbg_io("write %d bytes to PEB %d:%d", len, pnum, offset);
 
     ubi_assert(pnum >= 0 && pnum < ubi->peb_count);
     ubi_assert(offset >= 0 && offset + len <= ubi->peb_size);
     ubi_assert(offset % ubi->hdrs_min_io_size == 0);
     ubi_assert(len > 0 && len % ubi->hdrs_min_io_size == 0);
 
     if (ubi->ro_mode) {
         ubi_err(ubi, "read-only mode");
         return -EROFS;
     }
 
     err = self_check_not_bad(ubi, pnum);
     if (err)
         return err;
 
     /* The area we are writing to has to contain all 0xFF bytes */
     err = ubi_self_check_all_ff(ubi, pnum, offset, len);
     if (err)
         return err;
 
     if (offset >= ubi->leb_start) {
         /*
          * We write to the data area of the physical eraseblock. Make
          * sure it has valid EC and VID headers.
          */
         err = self_check_peb_ec_hdr(ubi, pnum);
         if (err)
             return err;
         err = self_check_peb_vid_hdr(ubi, pnum);
         if (err)
             return err;
     }
 
     if (ubi_dbg_is_write_failure(ubi)) {
         ubi_err(ubi, "cannot write %d bytes to PEB %d:%d (emulated)",
             len, pnum, offset);
         dump_stack();
         return -EIO;
     }
 
     addr = (loff_t)pnum * ubi->peb_size + offset;
     err = mtd_write(ubi->mtd, addr, len, &written, buf);
     if (err) {
         ubi_err(ubi, "error %d while writing %d bytes to PEB %d:%d, written %zd bytes",
             err, len, pnum, offset, written);
         dump_stack();
         ubi_dump_flash(ubi, pnum, offset, len);
     } else
         ubi_assert(written == len);
 
     if (!err) {
         err = self_check_write(ubi, buf, pnum, offset, len);
         if (err)
             return err;
 
         /*
          * Since we always write sequentially, the rest of the PEB has
          * to contain only 0xFF bytes.
          */
         offset += len;
         len = ubi->peb_size - offset;
         if (len)
             err = ubi_self_check_all_ff(ubi, pnum, offset, len);
     }
 
     return err;
 }
 
 /**
  * do_sync_erase - synchronously erase a physical eraseblock.
  * @ubi: UBI device description object
  * @pnum: the physical eraseblock number to erase
  *
  * This function synchronously erases physical eraseblock @pnum and returns
  * zero in case of success and a negative error code in case of failure. If
  * %-EIO is returned, the physical eraseblock most probably went bad.
  */
 static int do_sync_erase(struct ubi_device *ubi, int pnum)
 {
     int err, retries = 0;
     struct erase_info ei;
 
     dbg_io("erase PEB %d", pnum);
     ubi_assert(pnum >= 0 && pnum < ubi->peb_count);
 
     if (ubi->ro_mode) {
         ubi_err(ubi, "read-only mode");
         return -EROFS;
     }
 
 retry:
     memset(&ei, 0, sizeof(struct erase_info));
 
     ei.addr     = (loff_t)pnum * ubi->peb_size;
     ei.len      = ubi->peb_size;
 
     err = mtd_erase(ubi->mtd, &ei);
     if (err) {
         if (retries++ < UBI_IO_RETRIES) {
             ubi_warn(ubi, "error %d while erasing PEB %d, retry",
                  err, pnum);
             yield();
             goto retry;
         }
         ubi_err(ubi, "cannot erase PEB %d, error %d", pnum, err);
         dump_stack();
         return err;
     }
 
     err = ubi_self_check_all_ff(ubi, pnum, 0, ubi->peb_size);
     if (err)
         return err;
 
     if (ubi_dbg_is_erase_failure(ubi)) {
         ubi_err(ubi, "cannot erase PEB %d (emulated)", pnum);
         return -EIO;
     }
 
     return 0;
 }
 
 /* Patterns to write to a physical eraseblock when torturing it */
 static uint8_t patterns[] = {0xa5, 0x5a, 0x0};
 
 /**
  * torture_peb - test a supposedly bad physical eraseblock.
  * @ubi: UBI device description object
  * @pnum: the physical eraseblock number to test
  *
  * This function returns %-EIO if the physical eraseblock did not pass the
  * test, a positive number of erase operations done if the test was
  * successfully passed, and other negative error codes in case of other errors.
  */
 static int torture_peb(struct ubi_device *ubi, int pnum)
 {
     int err, i, patt_count;
 
     ubi_msg(ubi, "run torture test for PEB %d", pnum);
     patt_count = ARRAY_SIZE(patterns);
     ubi_assert(patt_count > 0);
 
     mutex_lock(&ubi->buf_mutex);
     for (i = 0; i < patt_count; i++) {
         err = do_sync_erase(ubi, pnum);
         if (err)
             goto out;
 
         /* Make sure the PEB contains only 0xFF bytes */
         err = ubi_io_read(ubi, ubi->peb_buf, pnum, 0, ubi->peb_size);
         if (err)
             goto out;
 
         err = ubi_check_pattern(ubi->peb_buf, 0xFF, ubi->peb_size);
         if (err == 0) {
             ubi_err(ubi, "erased PEB %d, but a non-0xFF byte found",
                 pnum);
             err = -EIO;
             goto out;
         }
 
         /* Write a pattern and check it */
         memset(ubi->peb_buf, patterns[i], ubi->peb_size);
         err = ubi_io_write(ubi, ubi->peb_buf, pnum, 0, ubi->peb_size);
         if (err)
             goto out;
 
         memset(ubi->peb_buf, ~patterns[i], ubi->peb_size);
         err = ubi_io_read(ubi, ubi->peb_buf, pnum, 0, ubi->peb_size);
         if (err)
             goto out;
 
         err = ubi_check_pattern(ubi->peb_buf, patterns[i],
                     ubi->peb_size);
         if (err == 0) {
             ubi_err(ubi, "pattern %x checking failed for PEB %d",
                 patterns[i], pnum);
             err = -EIO;
             goto out;
         }
     }
 
     err = patt_count;
     ubi_msg(ubi, "PEB %d passed torture test, do not mark it as bad", pnum);
 
 out:
     mutex_unlock(&ubi->buf_mutex);
     if (err == UBI_IO_BITFLIPS || mtd_is_eccerr(err)) {
         /*
          * If a bit-flip or data integrity error was detected, the test
          * has not passed because it happened on a freshly erased
          * physical eraseblock which means something is wrong with it.
          */
         ubi_err(ubi, "read problems on freshly erased PEB %d, must be bad",
             pnum);
         err = -EIO;
     }
     return err;
 }
 
 /**
  * nor_erase_prepare - prepare a NOR flash PEB for erasure.
  * @ubi: UBI device description object
  * @pnum: physical eraseblock number to prepare
  *
  * NOR flash, or at least some of them, have peculiar embedded PEB erasure
  * algorithm: the PEB is first filled with zeroes, then it is erased. And
  * filling with zeroes starts from the end of the PEB. This was observed with
  * Spansion S29GL512N NOR flash.
  *
  * This means that in case of a power cut we may end up with intact data at the
  * beginning of the PEB, and all zeroes at the end of PEB. In other words, the
  * EC and VID headers are OK, but a large chunk of data at the end of PEB is
  * zeroed. This makes UBI mistakenly treat this PEB as used and associate it
  * with an LEB, which leads to subsequent failures (e.g., UBIFS fails).
  *
  * This function is called before erasing NOR PEBs and it zeroes out EC and VID
  * magic numbers in order to invalidate them and prevent the failures. Returns
  * zero in case of success and a negative error code in case of failure.
  */
 static int nor_erase_prepare(struct ubi_device *ubi, int pnum)
 {
     int err;
     size_t written;
     loff_t addr;
     uint32_t data = 0;
     struct ubi_ec_hdr ec_hdr;
     struct ubi_vid_io_buf vidb;
 
     /*
      * Note, we cannot generally define VID header buffers on stack,
      * because of the way we deal with these buffers (see the header
      * comment in this file). But we know this is a NOR-specific piece of
      * code, so we can do this. But yes, this is error-prone and we should
      * (pre-)allocate VID header buffer instead.
      */
     struct ubi_vid_hdr vid_hdr;
 
     /*
      * If VID or EC is valid, we have to corrupt them before erasing.
      * It is important to first invalidate the EC header, and then the VID
      * header. Otherwise a power cut may lead to valid EC header and
      * invalid VID header, in which case UBI will treat this PEB as
      * corrupted and will try to preserve it, and print scary warnings.
      */
     addr = (loff_t)pnum * ubi->peb_size;
     err = ubi_io_read_ec_hdr(ubi, pnum, &ec_hdr, 0);
     if (err != UBI_IO_BAD_HDR_EBADMSG && err != UBI_IO_BAD_HDR &&
         err != UBI_IO_FF){
         err = mtd_write(ubi->mtd, addr, 4, &written, (void *)&data);
         if(err)
             goto error;
     }
 
     ubi_init_vid_buf(ubi, &vidb, &vid_hdr);
     ubi_assert(&vid_hdr == ubi_get_vid_hdr(&vidb));
 
     err = ubi_io_read_vid_hdr(ubi, pnum, &vidb, 0);
     if (err != UBI_IO_BAD_HDR_EBADMSG && err != UBI_IO_BAD_HDR &&
         err != UBI_IO_FF){
         addr += ubi->vid_hdr_aloffset;
         err = mtd_write(ubi->mtd, addr, 4, &written, (void *)&data);
         if (err)
             goto error;
     }
     return 0;
 
 error:
     /*
      * The PEB contains a valid VID or EC header, but we cannot invalidate
      * it. Supposedly the flash media or the driver is screwed up, so
      * return an error.
      */
     ubi_err(ubi, "cannot invalidate PEB %d, write returned %d", pnum, err);
     ubi_dump_flash(ubi, pnum, 0, ubi->peb_size);
     return -EIO;
 }
 
 /**
  * ubi_io_sync_erase - synchronously erase a physical eraseblock.
  * @ubi: UBI device description object
  * @pnum: physical eraseblock number to erase
  * @torture: if this physical eraseblock has to be tortured
  *
  * This function synchronously erases physical eraseblock @pnum. If @torture
  * flag is not zero, the physical eraseblock is checked by means of writing
  * different patterns to it and reading them back. If the torturing is enabled,
  * the physical eraseblock is erased more than once.
  *
  * This function returns the number of erasures made in case of success, %-EIO
  * if the erasure failed or the torturing test failed, and other negative error
  * codes in case of other errors. Note, %-EIO means that the physical
  * eraseblock is bad.
  */
 int ubi_io_sync_erase(struct ubi_device *ubi, int pnum, int torture)
 {
     int err, ret = 0;
 
     ubi_assert(pnum >= 0 && pnum < ubi->peb_count);
 
     err = self_check_not_bad(ubi, pnum);
     if (err != 0)
         return err;
 
     if (ubi->ro_mode) {
         ubi_err(ubi, "read-only mode");
         return -EROFS;
     }
 
     /*
      * If the flash is ECC-ed then we have to erase the ECC block before we
      * can write to it. But the write is in preparation to an erase in the
      * first place. This means we cannot zero out EC and VID before the
      * erase and we just have to hope the flash starts erasing from the
      * start of the page.
      */
     if (ubi->nor_flash && ubi->mtd->writesize == 1) {
         err = nor_erase_prepare(ubi, pnum);
         if (err)
             return err;
     }
 
     if (torture) {
         ret = torture_peb(ubi, pnum);
         if (ret < 0)
             return ret;
     }
 
     err = do_sync_erase(ubi, pnum);
     if (err)
         return err;
 
     return ret + 1;
 }
 
 /**
  * ubi_io_is_bad - check if a physical eraseblock is bad.
  * @ubi: UBI device description object
  * @pnum: the physical eraseblock number to check
  *
  * This function returns a positive number if the physical eraseblock is bad,
  * zero if not, and a negative error code if an error occurred.
  */
 int ubi_io_is_bad(const struct ubi_device *ubi, int pnum)
 {
     struct mtd_info *mtd = ubi->mtd;
 
     ubi_assert(pnum >= 0 && pnum < ubi->peb_count);
 
     if (ubi->bad_allowed) {
         int ret;
 
         ret = mtd_block_isbad(mtd, (loff_t)pnum * ubi->peb_size);
         if (ret < 0)
             ubi_err(ubi, "error %d while checking if PEB %d is bad",
                 ret, pnum);
         else if (ret)
             dbg_io("PEB %d is bad", pnum);
         return ret;
     }
 
     return 0;
 }
 
 /**
  * ubi_io_mark_bad - mark a physical eraseblock as bad.
  * @ubi: UBI device description object
  * @pnum: the physical eraseblock number to mark
  *
  * This function returns zero in case of success and a negative error code in
  * case of failure.
  */
 int ubi_io_mark_bad(const struct ubi_device *ubi, int pnum)
 {
     int err;
     struct mtd_info *mtd = ubi->mtd;
 
     ubi_assert(pnum >= 0 && pnum < ubi->peb_count);
 
     if (ubi->ro_mode) {
         ubi_err(ubi, "read-only mode");
         return -EROFS;
     }
 
     if (!ubi->bad_allowed)
         return 0;
 
     err = mtd_block_markbad(mtd, (loff_t)pnum * ubi->peb_size);
     if (err)
         ubi_err(ubi, "cannot mark PEB %d bad, error %d", pnum, err);
     return err;
 }
 
 /**
  * validate_ec_hdr - validate an erase counter header.
  * @ubi: UBI device description object
  * @ec_hdr: the erase counter header to check
  *
  * This function returns zero if the erase counter header is OK, and %1 if
  * not.
  */
 static int validate_ec_hdr(const struct ubi_device *ubi,
                const struct ubi_ec_hdr *ec_hdr)
 {
     long long ec;
     int vid_hdr_offset, leb_start;
 
     ec = be64_to_cpu(ec_hdr->ec);
     vid_hdr_offset = be32_to_cpu(ec_hdr->vid_hdr_offset);
     leb_start = be32_to_cpu(ec_hdr->data_offset);
 
     if (ec_hdr->version != UBI_VERSION) {
         ubi_err(ubi, "node with incompatible UBI version found: this UBI version is %d, image version is %d",
             UBI_VERSION, (int)ec_hdr->version);
         goto bad;
     }
 
     if (vid_hdr_offset != ubi->vid_hdr_offset) {
         ubi_err(ubi, "bad VID header offset %d, expected %d",
             vid_hdr_offset, ubi->vid_hdr_offset);
         goto bad;
     }
 
     if (leb_start != ubi->leb_start) {
         ubi_err(ubi, "bad data offset %d, expected %d",
             leb_start, ubi->leb_start);
         goto bad;
     }
 
     if (ec < 0 || ec > UBI_MAX_ERASECOUNTER) {
         ubi_err(ubi, "bad erase counter %lld", ec);
         goto bad;
     }
 
     return 0;
 
 bad:
     ubi_err(ubi, "bad EC header");
     ubi_dump_ec_hdr(ec_hdr);
     dump_stack();
     return 1;
 }
 
 /**
  * ubi_io_read_ec_hdr - read and check an erase counter header.
  * @ubi: UBI device description object
  * @pnum: physical eraseblock to read from
  * @ec_hdr: a &struct ubi_ec_hdr object where to store the read erase counter
  * header
  * @verbose: be verbose if the header is corrupted or was not found
  *
  * This function reads erase counter header from physical eraseblock @pnum and
  * stores it in @ec_hdr. This function also checks CRC checksum of the read
  * erase counter header. The following codes may be returned:
  *
  * o %0 if the CRC checksum is correct and the header was successfully read;
  * o %UBI_IO_BITFLIPS if the CRC is correct, but bit-flips were detected
  *   and corrected by the flash driver; this is harmless but may indicate that
  *   this eraseblock may become bad soon (but may be not);
  * o %UBI_IO_BAD_HDR if the erase counter header is corrupted (a CRC error);
  * o %UBI_IO_BAD_HDR_EBADMSG is the same as %UBI_IO_BAD_HDR, but there also was
  *   a data integrity error (uncorrectable ECC error in case of NAND);
  * o %UBI_IO_FF if only 0xFF bytes were read (the PEB is supposedly empty)
  * o a negative error code in case of failure.
  */
 int ubi_io_read_ec_hdr(struct ubi_device *ubi, int pnum,
                struct ubi_ec_hdr *ec_hdr, int verbose)
 {
     int err, read_err;
     uint32_t crc, magic, hdr_crc;
 
     dbg_io("read EC header from PEB %d", pnum);
     ubi_assert(pnum >= 0 && pnum < ubi->peb_count);
 
     read_err = ubi_io_read(ubi, ec_hdr, pnum, 0, UBI_EC_HDR_SIZE);
     if (read_err) {
         if (read_err != UBI_IO_BITFLIPS && !mtd_is_eccerr(read_err))
             return read_err;
 
         /*
          * We read all the data, but either a correctable bit-flip
          * occurred, or MTD reported a data integrity error
          * (uncorrectable ECC error in case of NAND). The former is
          * harmless, the later may mean that the read data is
          * corrupted. But we have a CRC check-sum and we will detect
          * this. If the EC header is still OK, we just report this as
          * there was a bit-flip, to force scrubbing.
          */
     }
 
     magic = be32_to_cpu(ec_hdr->magic);
     if (magic != UBI_EC_HDR_MAGIC) {
         if (mtd_is_eccerr(read_err))
             return UBI_IO_BAD_HDR_EBADMSG;
 
         /*
          * The magic field is wrong. Let's check if we have read all
          * 0xFF. If yes, this physical eraseblock is assumed to be
          * empty.
          */
         if (ubi_check_pattern(ec_hdr, 0xFF, UBI_EC_HDR_SIZE)) {
             /* The physical eraseblock is supposedly empty */
             if (verbose)
                 ubi_warn(ubi, "no EC header found at PEB %d, only 0xFF bytes",
                      pnum);
             dbg_bld("no EC header found at PEB %d, only 0xFF bytes",
                 pnum);
             if (!read_err)
                 return UBI_IO_FF;
             else
                 return UBI_IO_FF_BITFLIPS;
         }
 
         /*
          * This is not a valid erase counter header, and these are not
          * 0xFF bytes. Report that the header is corrupted.
          */
         if (verbose) {
             ubi_warn(ubi, "bad magic number at PEB %d: %08x instead of %08x",
                  pnum, magic, UBI_EC_HDR_MAGIC);
             ubi_dump_ec_hdr(ec_hdr);
         }
         dbg_bld("bad magic number at PEB %d: %08x instead of %08x",
             pnum, magic, UBI_EC_HDR_MAGIC);
         return UBI_IO_BAD_HDR;
     }
 
     crc = crc32(UBI_CRC32_INIT, ec_hdr, UBI_EC_HDR_SIZE_CRC);
     hdr_crc = be32_to_cpu(ec_hdr->hdr_crc);
 
     if (hdr_crc != crc) {
         if (verbose) {
             ubi_warn(ubi, "bad EC header CRC at PEB %d, calculated %#08x, read %#08x",
                  pnum, crc, hdr_crc);
             ubi_dump_ec_hdr(ec_hdr);
         }
         dbg_bld("bad EC header CRC at PEB %d, calculated %#08x, read %#08x",
             pnum, crc, hdr_crc);
 
         if (!read_err)
             return UBI_IO_BAD_HDR;
         else
             return UBI_IO_BAD_HDR_EBADMSG;
     }
 
     /* And of course validate what has just been read from the media */
     err = validate_ec_hdr(ubi, ec_hdr);
     if (err) {
         ubi_err(ubi, "validation failed for PEB %d", pnum);
         return -EINVAL;
     }
 
     /*
      * If there was %-EBADMSG, but the header CRC is still OK, report about
      * a bit-flip to force scrubbing on this PEB.
      */
     return read_err ? UBI_IO_BITFLIPS : 0;
 }
 
 /**
  * ubi_io_write_ec_hdr - write an erase counter header.
  * @ubi: UBI device description object
  * @pnum: physical eraseblock to write to
  * @ec_hdr: the erase counter header to write
  *
  * This function writes erase counter header described by @ec_hdr to physical
  * eraseblock @pnum. It also fills most fields of @ec_hdr before writing, so
  * the caller do not have to fill them. Callers must only fill the @ec_hdr->ec
  * field.
  *
  * This function returns zero in case of success and a negative error code in
  * case of failure. If %-EIO is returned, the physical eraseblock most probably
  * went bad.
  */
 int ubi_io_write_ec_hdr(struct ubi_device *ubi, int pnum,
             struct ubi_ec_hdr *ec_hdr)
 {
     int err;
     uint32_t crc;
 
     dbg_io("write EC header to PEB %d", pnum);
     ubi_assert(pnum >= 0 &&  pnum < ubi->peb_count);
 
     ec_hdr->magic = cpu_to_be32(UBI_EC_HDR_MAGIC);
     ec_hdr->version = UBI_VERSION;
     ec_hdr->vid_hdr_offset = cpu_to_be32(ubi->vid_hdr_offset);
     ec_hdr->data_offset = cpu_to_be32(ubi->leb_start);
     ec_hdr->image_seq = cpu_to_be32(ubi->image_seq);
     crc = crc32(UBI_CRC32_INIT, ec_hdr, UBI_EC_HDR_SIZE_CRC);
     ec_hdr->hdr_crc = cpu_to_be32(crc);
 
     err = self_check_ec_hdr(ubi, pnum, ec_hdr);
     if (err)
         return err;
 
     if (ubi_dbg_power_cut(ubi, POWER_CUT_EC_WRITE))
         return -EROFS;
 
     err = ubi_io_write(ubi, ec_hdr, pnum, 0, ubi->ec_hdr_alsize);
     return err;
 }
 
 /**
  * validate_vid_hdr - validate a volume identifier header.
  * @ubi: UBI device description object
  * @vid_hdr: the volume identifier header to check
  *
  * This function checks that data stored in the volume identifier header
  * @vid_hdr. Returns zero if the VID header is OK and %1 if not.
  */
 static int validate_vid_hdr(const struct ubi_device *ubi,
                 const struct ubi_vid_hdr *vid_hdr)
 {
     int vol_type = vid_hdr->vol_type;
     int copy_flag = vid_hdr->copy_flag;
     int vol_id = be32_to_cpu(vid_hdr->vol_id);
     int lnum = be32_to_cpu(vid_hdr->lnum);
     int compat = vid_hdr->compat;
     int data_size = be32_to_cpu(vid_hdr->data_size);
     int used_ebs = be32_to_cpu(vid_hdr->used_ebs);
     int data_pad = be32_to_cpu(vid_hdr->data_pad);
     int data_crc = be32_to_cpu(vid_hdr->data_crc);
     int usable_leb_size = ubi->leb_size - data_pad;
 
     if (copy_flag != 0 && copy_flag != 1) {
         ubi_err(ubi, "bad copy_flag");
         goto bad;
     }
 
     if (vol_id < 0 || lnum < 0 || data_size < 0 || used_ebs < 0 ||
         data_pad < 0) {
         ubi_err(ubi, "negative values");
         goto bad;
     }
 
     if (vol_id >= UBI_MAX_VOLUMES && vol_id < UBI_INTERNAL_VOL_START) {
         ubi_err(ubi, "bad vol_id");
         goto bad;
     }
 
     if (vol_id < UBI_INTERNAL_VOL_START && compat != 0) {
         ubi_err(ubi, "bad compat");
         goto bad;
     }
 
     if (vol_id >= UBI_INTERNAL_VOL_START && compat != UBI_COMPAT_DELETE &&
         compat != UBI_COMPAT_RO && compat != UBI_COMPAT_PRESERVE &&
         compat != UBI_COMPAT_REJECT) {
         ubi_err(ubi, "bad compat");
         goto bad;
     }
 
     if (vol_type != UBI_VID_DYNAMIC && vol_type != UBI_VID_STATIC) {
         ubi_err(ubi, "bad vol_type");
         goto bad;
     }
 
     if (data_pad >= ubi->leb_size / 2) {
         ubi_err(ubi, "bad data_pad");
         goto bad;
     }
 
     if (data_size > ubi->leb_size) {
         ubi_err(ubi, "bad data_size");
         goto bad;
     }
 
     if (vol_type == UBI_VID_STATIC) {
         /*
          * Although from high-level point of view static volumes may
          * contain zero bytes of data, but no VID headers can contain
          * zero at these fields, because they empty volumes do not have
          * mapped logical eraseblocks.
          */
         if (used_ebs == 0) {
             ubi_err(ubi, "zero used_ebs");
             goto bad;
         }
         if (data_size == 0) {
             ubi_err(ubi, "zero data_size");
             goto bad;
         }
         if (lnum < used_ebs - 1) {
             if (data_size != usable_leb_size) {
                 ubi_err(ubi, "bad data_size");
                 goto bad;
             }
         } else if (lnum > used_ebs - 1) {
             ubi_err(ubi, "too high lnum");
             goto bad;
         }
     } else {
         if (copy_flag == 0) {
             if (data_crc != 0) {
                 ubi_err(ubi, "non-zero data CRC");
                 goto bad;
             }
             if (data_size != 0) {
                 ubi_err(ubi, "non-zero data_size");
                 goto bad;
             }
         } else {
             if (data_size == 0) {
                 ubi_err(ubi, "zero data_size of copy");
                 goto bad;
             }
         }
         if (used_ebs != 0) {
             ubi_err(ubi, "bad used_ebs");
             goto bad;
         }
     }
 
     return 0;
 
 bad:
     ubi_err(ubi, "bad VID header");
     ubi_dump_vid_hdr(vid_hdr);
     dump_stack();
     return 1;
 }
 
 /**
  * ubi_io_read_vid_hdr - read and check a volume identifier header.
  * @ubi: UBI device description object
  * @pnum: physical eraseblock number to read from
  * @vidb: the volume identifier buffer to store data in
  * @verbose: be verbose if the header is corrupted or wasn't found
  *
  * This function reads the volume identifier header from physical eraseblock
  * @pnum and stores it in @vidb. It also checks CRC checksum of the read
  * volume identifier header. The error codes are the same as in
  * 'ubi_io_read_ec_hdr()'.
  *
  * Note, the implementation of this function is also very similar to
  * 'ubi_io_read_ec_hdr()', so refer commentaries in 'ubi_io_read_ec_hdr()'.
  */
 int ubi_io_read_vid_hdr(struct ubi_device *ubi, int pnum,
             struct ubi_vid_io_buf *vidb, int verbose)
 {
     int err, read_err;
     uint32_t crc, magic, hdr_crc;
     struct ubi_vid_hdr *vid_hdr = ubi_get_vid_hdr(vidb);
     void *p = vidb->buffer;
 
     dbg_io("read VID header from PEB %d", pnum);
     ubi_assert(pnum >= 0 &&  pnum < ubi->peb_count);
 
     read_err = ubi_io_read(ubi, p, pnum, ubi->vid_hdr_aloffset,
               ubi->vid_hdr_shift + UBI_VID_HDR_SIZE);
     if (read_err && read_err != UBI_IO_BITFLIPS && !mtd_is_eccerr(read_err))
         return read_err;
 
     magic = be32_to_cpu(vid_hdr->magic);
     if (magic != UBI_VID_HDR_MAGIC) {
         if (mtd_is_eccerr(read_err))
             return UBI_IO_BAD_HDR_EBADMSG;
 
         if (ubi_check_pattern(vid_hdr, 0xFF, UBI_VID_HDR_SIZE)) {
             if (verbose)
                 ubi_warn(ubi, "no VID header found at PEB %d, only 0xFF bytes",
                      pnum);
             dbg_bld("no VID header found at PEB %d, only 0xFF bytes",
                 pnum);
             if (!read_err)
                 return UBI_IO_FF;
             else
                 return UBI_IO_FF_BITFLIPS;
         }
 
         if (verbose) {
             ubi_warn(ubi, "bad magic number at PEB %d: %08x instead of %08x",
                  pnum, magic, UBI_VID_HDR_MAGIC);
             ubi_dump_vid_hdr(vid_hdr);
         }
         dbg_bld("bad magic number at PEB %d: %08x instead of %08x",
             pnum, magic, UBI_VID_HDR_MAGIC);
         return UBI_IO_BAD_HDR;
     }
 
     crc = crc32(UBI_CRC32_INIT, vid_hdr, UBI_VID_HDR_SIZE_CRC);
     hdr_crc = be32_to_cpu(vid_hdr->hdr_crc);
 
     if (hdr_crc != crc) {
         if (verbose) {
             ubi_warn(ubi, "bad CRC at PEB %d, calculated %#08x, read %#08x",
                  pnum, crc, hdr_crc);
             ubi_dump_vid_hdr(vid_hdr);
         }
         dbg_bld("bad CRC at PEB %d, calculated %#08x, read %#08x",
             pnum, crc, hdr_crc);
         if (!read_err)
             return UBI_IO_BAD_HDR;
         else
             return UBI_IO_BAD_HDR_EBADMSG;
     }
 
     err = validate_vid_hdr(ubi, vid_hdr);
     if (err) {
         ubi_err(ubi, "validation failed for PEB %d", pnum);
         return -EINVAL;
     }
 
     return read_err ? UBI_IO_BITFLIPS : 0;
 }
 
 /**
  * ubi_io_write_vid_hdr - write a volume identifier header.
  * @ubi: UBI device description object
  * @pnum: the physical eraseblock number to write to
  * @vidb: the volume identifier buffer to write
  *
  * This function writes the volume identifier header described by @vid_hdr to
  * physical eraseblock @pnum. This function automatically fills the
  * @vidb->hdr->magic and the @vidb->hdr->version fields, as well as calculates
  * header CRC checksum and stores it at vidb->hdr->hdr_crc.
  *
  * This function returns zero in case of success and a negative error code in
  * case of failure. If %-EIO is returned, the physical eraseblock probably went
  * bad.
  */
 int ubi_io_write_vid_hdr(struct ubi_device *ubi, int pnum,
              struct ubi_vid_io_buf *vidb)
 {
     struct ubi_vid_hdr *vid_hdr = ubi_get_vid_hdr(vidb);
     int err;
     uint32_t crc;
     void *p = vidb->buffer;
 
     dbg_io("write VID header to PEB %d", pnum);
     ubi_assert(pnum >= 0 &&  pnum < ubi->peb_count);
 
     err = self_check_peb_ec_hdr(ubi, pnum);
     if (err)
         return err;
 
     vid_hdr->magic = cpu_to_be32(UBI_VID_HDR_MAGIC);
     vid_hdr->version = UBI_VERSION;
     crc = crc32(UBI_CRC32_INIT, vid_hdr, UBI_VID_HDR_SIZE_CRC);
     vid_hdr->hdr_crc = cpu_to_be32(crc);
 
     err = self_check_vid_hdr(ubi, pnum, vid_hdr);
     if (err)
         return err;
 
     if (ubi_dbg_power_cut(ubi, POWER_CUT_VID_WRITE))
         return -EROFS;
 
     err = ubi_io_write(ubi, p, pnum, ubi->vid_hdr_aloffset,
                ubi->vid_hdr_alsize);
     return err;
 }
 
 /**
  * self_check_not_bad - ensure that a physical eraseblock is not bad.
  * @ubi: UBI device description object
  * @pnum: physical eraseblock number to check
  *
  * This function returns zero if the physical eraseblock is good, %-EINVAL if
  * it is bad and a negative error code if an error occurred.
  */
 static int self_check_not_bad(const struct ubi_device *ubi, int pnum)
 {
     int err;
 
     if (!ubi_dbg_chk_io(ubi))
         return 0;
 
     err = ubi_io_is_bad(ubi, pnum);
     if (!err)
         return err;
 
     ubi_err(ubi, "self-check failed for PEB %d", pnum);
     dump_stack();
     return err > 0 ? -EINVAL : err;
 }
 
 /**
  * self_check_ec_hdr - check if an erase counter header is all right.
  * @ubi: UBI device description object
  * @pnum: physical eraseblock number the erase counter header belongs to
  * @ec_hdr: the erase counter header to check
  *
  * This function returns zero if the erase counter header contains valid
  * values, and %-EINVAL if not.
  */
 static int self_check_ec_hdr(const struct ubi_device *ubi, int pnum,
                  const struct ubi_ec_hdr *ec_hdr)
 {
     int err;
     uint32_t magic;
 
     if (!ubi_dbg_chk_io(ubi))
         return 0;
 
     magic = be32_to_cpu(ec_hdr->magic);
     if (magic != UBI_EC_HDR_MAGIC) {
         ubi_err(ubi, "bad magic %#08x, must be %#08x",
             magic, UBI_EC_HDR_MAGIC);
         goto fail;
     }
 
     err = validate_ec_hdr(ubi, ec_hdr);
     if (err) {
         ubi_err(ubi, "self-check failed for PEB %d", pnum);
         goto fail;
     }
 
     return 0;
 
 fail:
     ubi_dump_ec_hdr(ec_hdr);
     dump_stack();
     return -EINVAL;
 }
 
 /**
  * self_check_peb_ec_hdr - check erase counter header.
  * @ubi: UBI device description object
  * @pnum: the physical eraseblock number to check
  *
  * This function returns zero if the erase counter header is all right and and
  * a negative error code if not or if an error occurred.
  */
 static int self_check_peb_ec_hdr(const struct ubi_device *ubi, int pnum)
 {
     int err;
     uint32_t crc, hdr_crc;
     struct ubi_ec_hdr *ec_hdr;
 
     if (!ubi_dbg_chk_io(ubi))
         return 0;
 
     ec_hdr = kzalloc(ubi->ec_hdr_alsize, GFP_NOFS);
     if (!ec_hdr)
         return -ENOMEM;
 
     err = ubi_io_read(ubi, ec_hdr, pnum, 0, UBI_EC_HDR_SIZE);
     if (err && err != UBI_IO_BITFLIPS && !mtd_is_eccerr(err))
         goto exit;
 
     crc = crc32(UBI_CRC32_INIT, ec_hdr, UBI_EC_HDR_SIZE_CRC);
     hdr_crc = be32_to_cpu(ec_hdr->hdr_crc);
     if (hdr_crc != crc) {
         ubi_err(ubi, "bad CRC, calculated %#08x, read %#08x",
             crc, hdr_crc);
         ubi_err(ubi, "self-check failed for PEB %d", pnum);
         ubi_dump_ec_hdr(ec_hdr);
         dump_stack();
         err = -EINVAL;
         goto exit;
     }
 
     err = self_check_ec_hdr(ubi, pnum, ec_hdr);
 
 exit:
     kfree(ec_hdr);
     return err;
 }
 
 /**
  * self_check_vid_hdr - check that a volume identifier header is all right.
  * @ubi: UBI device description object
  * @pnum: physical eraseblock number the volume identifier header belongs to
  * @vid_hdr: the volume identifier header to check
  *
  * This function returns zero if the volume identifier header is all right, and
  * %-EINVAL if not.
  */
 static int self_check_vid_hdr(const struct ubi_device *ubi, int pnum,
                   const struct ubi_vid_hdr *vid_hdr)
 {
     int err;
     uint32_t magic;
 
     if (!ubi_dbg_chk_io(ubi))
         return 0;
 
     magic = be32_to_cpu(vid_hdr->magic);
     if (magic != UBI_VID_HDR_MAGIC) {
         ubi_err(ubi, "bad VID header magic %#08x at PEB %d, must be %#08x",
             magic, pnum, UBI_VID_HDR_MAGIC);
         goto fail;
     }
 
     err = validate_vid_hdr(ubi, vid_hdr);
     if (err) {
         ubi_err(ubi, "self-check failed for PEB %d", pnum);
         goto fail;
     }
 
     return err;
 
 fail:
     ubi_err(ubi, "self-check failed for PEB %d", pnum);
     ubi_dump_vid_hdr(vid_hdr);
     dump_stack();
     return -EINVAL;
 
 }
 
 /**
  * self_check_peb_vid_hdr - check volume identifier header.
  * @ubi: UBI device description object
  * @pnum: the physical eraseblock number to check
  *
  * This function returns zero if the volume identifier header is all right,
  * and a negative error code if not or if an error occurred.
  */
 static int self_check_peb_vid_hdr(const struct ubi_device *ubi, int pnum)
 {
     int err;
     uint32_t crc, hdr_crc;
     struct ubi_vid_io_buf *vidb;
     struct ubi_vid_hdr *vid_hdr;
     void *p;
 
     if (!ubi_dbg_chk_io(ubi))
         return 0;
 
     vidb = ubi_alloc_vid_buf(ubi, GFP_NOFS);
     if (!vidb)
         return -ENOMEM;
 
     vid_hdr = ubi_get_vid_hdr(vidb);
     p = vidb->buffer;
     err = ubi_io_read(ubi, p, pnum, ubi->vid_hdr_aloffset,
               ubi->vid_hdr_alsize);
     if (err && err != UBI_IO_BITFLIPS && !mtd_is_eccerr(err))
         goto exit;
 
     crc = crc32(UBI_CRC32_INIT, vid_hdr, UBI_VID_HDR_SIZE_CRC);
     hdr_crc = be32_to_cpu(vid_hdr->hdr_crc);
     if (hdr_crc != crc) {
         ubi_err(ubi, "bad VID header CRC at PEB %d, calculated %#08x, read %#08x",
             pnum, crc, hdr_crc);
         ubi_err(ubi, "self-check failed for PEB %d", pnum);
         ubi_dump_vid_hdr(vid_hdr);
         dump_stack();
         err = -EINVAL;
         goto exit;
     }
 
     err = self_check_vid_hdr(ubi, pnum, vid_hdr);
 
 exit:
     ubi_free_vid_buf(vidb);
     return err;
 }
 
 /**
  * self_check_write - make sure write succeeded.
  * @ubi: UBI device description object
  * @buf: buffer with data which were written
  * @pnum: physical eraseblock number the data were written to
  * @offset: offset within the physical eraseblock the data were written to
  * @len: how many bytes were written
  *
  * This functions reads data which were recently written and compares it with
  * the original data buffer - the data have to match. Returns zero if the data
  * match and a negative error code if not or in case of failure.
  */
 static int self_check_write(struct ubi_device *ubi, const void *buf, int pnum,
                 int offset, int len)
 {
     int err, i;
     size_t read;
     void *buf1;
     loff_t addr = (loff_t)pnum * ubi->peb_size + offset;
 
     if (!ubi_dbg_chk_io(ubi))
         return 0;
 
     buf1 = __vmalloc(len, GFP_NOFS);
     if (!buf1) {
         ubi_err(ubi, "cannot allocate memory to check writes");
         return 0;
     }
 
     err = mtd_read(ubi->mtd, addr, len, &read, buf1);
     if (err && !mtd_is_bitflip(err))
         goto out_free;
 
     for (i = 0; i < len; i++) {
         uint8_t c = ((uint8_t *)buf)[i];
         uint8_t c1 = ((uint8_t *)buf1)[i];
         int dump_len;
 
         if (c == c1)
             continue;
 
         ubi_err(ubi, "self-check failed for PEB %d:%d, len %d",
             pnum, offset, len);
         ubi_msg(ubi, "data differ at position %d", i);
         dump_len = max_t(int, 128, len - i);
         ubi_msg(ubi, "hex dump of the original buffer from %d to %d",
             i, i + dump_len);
         print_hex_dump(KERN_DEBUG, "", DUMP_PREFIX_OFFSET, 32, 1,
                    buf + i, dump_len, 1);
         ubi_msg(ubi, "hex dump of the read buffer from %d to %d",
             i, i + dump_len);
         print_hex_dump(KERN_DEBUG, "", DUMP_PREFIX_OFFSET, 32, 1,
                    buf1 + i, dump_len, 1);
         dump_stack();
         err = -EINVAL;
         goto out_free;
     }
 
     vfree(buf1);
     return 0;
 
 out_free:
     vfree(buf1);
     return err;
 }
 
 /**
  * ubi_self_check_all_ff - check that a region of flash is empty.
  * @ubi: UBI device description object
  * @pnum: the physical eraseblock number to check
  * @offset: the starting offset within the physical eraseblock to check
  * @len: the length of the region to check
  *
  * This function returns zero if only 0xFF bytes are present at offset
  * @offset of the physical eraseblock @pnum, and a negative error code if not
  * or if an error occurred.
  */
 int ubi_self_check_all_ff(struct ubi_device *ubi, int pnum, int offset, int len)
 {
     size_t read;
     int err;
     void *buf;
     loff_t addr = (loff_t)pnum * ubi->peb_size + offset;
 
     if (!ubi_dbg_chk_io(ubi))
         return 0;
 
     buf = __vmalloc(len, GFP_NOFS);
     if (!buf) {
         ubi_err(ubi, "cannot allocate memory to check for 0xFFs");
         return 0;
     }
 
     err = mtd_read(ubi->mtd, addr, len, &read, buf);
     if (err && !mtd_is_bitflip(err)) {
         ubi_err(ubi, "err %d while reading %d bytes from PEB %d:%d, read %zd bytes",
             err, len, pnum, offset, read);
         goto error;
     }
 
     err = ubi_check_pattern(buf, 0xFF, len);
     if (err == 0) {
         ubi_err(ubi, "flash region at PEB %d:%d, length %d does not contain all 0xFF bytes",
             pnum, offset, len);
         goto fail;
     }
 
     vfree(buf);
     return 0;
 
 fail:
     ubi_err(ubi, "self-check failed for PEB %d", pnum);
     ubi_msg(ubi, "hex dump of the %d-%d region", offset, offset + len);
     print_hex_dump(KERN_DEBUG, "", DUMP_PREFIX_OFFSET, 32, 1, buf, len, 1);
     err = -EINVAL;
 error:
     dump_stack();
     vfree(buf);
     return err;
 }

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