fs/qnx4/dir.c

0001 // SPDX-License-Identifier: GPL-2.0
0002 /*
0003  * QNX4 file system, Linux implementation.
0004  *
0005  * Version : 0.2.1
0006  *
0007  * Using parts of the xiafs filesystem.
0008  *
0009  * History :
0010  *
0011  * 28-05-1998 by Richard Frowijn : first release.
0012  * 20-06-1998 by Frank Denis : Linux 2.1.99+ & dcache support.
0013  */
0014
0015 #include <linux/buffer_head.h>
0016 #include "qnx4.h"
0017
0018 /*
0019  * A qnx4 directory entry is an inode entry or link info
0020  * depending on the status field in the last byte. The
0021  * first byte is where the name start either way, and a
0022  * zero means it's empty.
0023  *
0024  * Also, due to a bug in gcc, we don't want to use the
0025  * real (differently sized) name arrays in the inode and
0026  * link entries, but always the 'de_name[]' one in the
0027  * fake struct entry.
0028  *
0029  * See
0030  *
0031  *   https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99578#c6
0032  *
0033  * for details, but basically gcc will take the size of the
0034  * 'name' array from one of the used union entries randomly.
0035  *
0036  * This use of 'de_name[]' (48 bytes) avoids the false positive
0037  * warnings that would happen if gcc decides to use 'inode.di_name'
0038  * (16 bytes) even when the pointer and size were to come from
0039  * 'link.dl_name' (48 bytes).
0040  *
0041  * In all cases the actual name pointer itself is the same, it's
0042  * only the gcc internal 'what is the size of this field' logic
0043  * that can get confused.
0044  */
0045 union qnx4_directory_entry {
0046     struct {
0047         const char de_name[48];
0048         u8 de_pad[15];
0049         u8 de_status;
0050     };
0051     struct qnx4_inode_entry inode;
0052     struct qnx4_link_info link;
0053 };
0054
0055 static int qnx4_readdir(struct file *file, struct dir_context *ctx)
0056 {
0057     struct inode *inode = file_inode(file);
0058     unsigned int offset;
0059     struct buffer_head *bh;
0060     unsigned long blknum;
0061     int ix, ino;
0062     int size;
0063
0064     QNX4DEBUG((KERN_INFO "qnx4_readdir:i_size = %ld\n", (long) inode->i_size));
0065     QNX4DEBUG((KERN_INFO "pos                 = %ld\n", (long) ctx->pos));
0066
0067     while (ctx->pos < inode->i_size) {
0068         blknum = qnx4_block_map(inode, ctx->pos >> QNX4_BLOCK_SIZE_BITS);
0069         bh = sb_bread(inode->i_sb, blknum);
0070         if (bh == NULL) {
0071             printk(KERN_ERR "qnx4_readdir: bread failed (%ld)\n", blknum);
0072             return 0;
0073         }
0074         ix = (ctx->pos >> QNX4_DIR_ENTRY_SIZE_BITS) % QNX4_INODES_PER_BLOCK;
0075         for (; ix < QNX4_INODES_PER_BLOCK; ix++, ctx->pos += QNX4_DIR_ENTRY_SIZE) {
0076             union qnx4_directory_entry *de;
0077
0078             offset = ix * QNX4_DIR_ENTRY_SIZE;
0079             de = (union qnx4_directory_entry *) (bh->b_data + offset);
0080
0081             if (!de->de_name[0])
0082                 continue;
0083             if (!(de->de_status & (QNX4_FILE_USED|QNX4_FILE_LINK)))
0084                 continue;
0085             if (!(de->de_status & QNX4_FILE_LINK)) {
0086                 size = sizeof(de->inode.di_fname);
0087                 ino = blknum * QNX4_INODES_PER_BLOCK + ix - 1;
0088             } else {
0089                 size = sizeof(de->link.dl_fname);
0090                 ino = ( le32_to_cpu(de->link.dl_inode_blk) - 1 ) *
0091                     QNX4_INODES_PER_BLOCK +
0092                     de->link.dl_inode_ndx;
0093             }
0094             size = strnlen(de->de_name, size);
0095             QNX4DEBUG((KERN_INFO "qnx4_readdir:%.*s\n", size, name));
0096             if (!dir_emit(ctx, de->de_name, size, ino, DT_UNKNOWN)) {
0097                 brelse(bh);
0098                 return 0;
0099             }
0100         }
0101         brelse(bh);
0102     }
0103     return 0;
0104 }
0105
0106 const struct file_operations qnx4_dir_operations =
0107 {
0108     .llseek     = generic_file_llseek,
0109     .read       = generic_read_dir,
0110     .iterate_shared = qnx4_readdir,
0111     .fsync      = generic_file_fsync,
0112 };
0113
0114 const struct inode_operations qnx4_dir_inode_operations =
0115 {
0116     .lookup     = qnx4_lookup,
0117 };