include/linux/tty_ldisc.h

0001 /* SPDX-License-Identifier: GPL-2.0 */
0002 #ifndef _LINUX_TTY_LDISC_H
0003 #define _LINUX_TTY_LDISC_H
0004
0005 struct tty_struct;
0006
0007 #include <linux/fs.h>
0008 #include <linux/wait.h>
0009 #include <linux/atomic.h>
0010 #include <linux/list.h>
0011 #include <linux/lockdep.h>
0012 #include <linux/seq_file.h>
0013
0014 /*
0015  * the semaphore definition
0016  */
0017 struct ld_semaphore {
0018     atomic_long_t       count;
0019     raw_spinlock_t      wait_lock;
0020     unsigned int        wait_readers;
0021     struct list_head    read_wait;
0022     struct list_head    write_wait;
0023 #ifdef CONFIG_DEBUG_LOCK_ALLOC
0024     struct lockdep_map  dep_map;
0025 #endif
0026 };
0027
0028 void __init_ldsem(struct ld_semaphore *sem, const char *name,
0029              struct lock_class_key *key);
0030
0031 #define init_ldsem(sem)                     \
0032 do {                                \
0033     static struct lock_class_key __key;         \
0034                                 \
0035     __init_ldsem((sem), #sem, &__key);          \
0036 } while (0)
0037
0038
0039 int ldsem_down_read(struct ld_semaphore *sem, long timeout);
0040 int ldsem_down_read_trylock(struct ld_semaphore *sem);
0041 int ldsem_down_write(struct ld_semaphore *sem, long timeout);
0042 int ldsem_down_write_trylock(struct ld_semaphore *sem);
0043 void ldsem_up_read(struct ld_semaphore *sem);
0044 void ldsem_up_write(struct ld_semaphore *sem);
0045
0046 #ifdef CONFIG_DEBUG_LOCK_ALLOC
0047 int ldsem_down_read_nested(struct ld_semaphore *sem, int subclass,
0048         long timeout);
0049 int ldsem_down_write_nested(struct ld_semaphore *sem, int subclass,
0050         long timeout);
0051 #else
0052 # define ldsem_down_read_nested(sem, subclass, timeout)     \
0053         ldsem_down_read(sem, timeout)
0054 # define ldsem_down_write_nested(sem, subclass, timeout)    \
0055         ldsem_down_write(sem, timeout)
0056 #endif
0057
0058 /**
0059  * struct tty_ldisc_ops - ldisc operations
0060  *
0061  * @name: name of this ldisc rendered in /proc/tty/ldiscs
0062  * @num: ``N_*`` number (%N_TTY, %N_HDLC, ...) reserved to this ldisc
0063  *
0064  * @open: [TTY] ``int ()(struct tty_struct *tty)``
0065  *
0066  *  This function is called when the line discipline is associated with the
0067  *  @tty. No other call into the line discipline for this tty will occur
0068  *  until it completes successfully. It should initialize any state needed
0069  *  by the ldisc, and set @tty->receive_room to the maximum amount of data
0070  *  the line discipline is willing to accept from the driver with a single
0071  *  call to @receive_buf(). Returning an error will prevent the ldisc from
0072  *  being attached.
0073  *
0074  *  Can sleep.
0075  *
0076  * @close: [TTY] ``void ()(struct tty_struct *tty)``
0077  *
0078  *  This function is called when the line discipline is being shutdown,
0079  *  either because the @tty is being closed or because the @tty is being
0080  *  changed to use a new line discipline. At the point of execution no
0081  *  further users will enter the ldisc code for this tty.
0082  *
0083  *  Can sleep.
0084  *
0085  * @flush_buffer: [TTY] ``void ()(struct tty_struct *tty)``
0086  *
0087  *  This function instructs the line discipline to clear its buffers of any
0088  *  input characters it may have queued to be delivered to the user mode
0089  *  process. It may be called at any point between open and close.
0090  *
0091  * @read: [TTY] ``ssize_t ()(struct tty_struct *tty, struct file *file,
0092  *      unsigned char *buf, size_t nr)``
0093  *
0094  *  This function is called when the user requests to read from the @tty.
0095  *  The line discipline will return whatever characters it has buffered up
0096  *  for the user. If this function is not defined, the user will receive
0097  *  an %EIO error. Multiple read calls may occur in parallel and the ldisc
0098  *  must deal with serialization issues.
0099  *
0100  *  Can sleep.
0101  *
0102  * @write: [TTY] ``ssize_t ()(struct tty_struct *tty, struct file *file,
0103  *      const unsigned char *buf, size_t nr)``
0104  *
0105  *  This function is called when the user requests to write to the @tty.
0106  *  The line discipline will deliver the characters to the low-level tty
0107  *  device for transmission, optionally performing some processing on the
0108  *  characters first. If this function is not defined, the user will
0109  *  receive an %EIO error.
0110  *
0111  *  Can sleep.
0112  *
0113  * @ioctl: [TTY] ``int ()(struct tty_struct *tty, unsigned int cmd,
0114  *      unsigned long arg)``
0115  *
0116  *  This function is called when the user requests an ioctl which is not
0117  *  handled by the tty layer or the low-level tty driver. It is intended
0118  *  for ioctls which affect line discpline operation.  Note that the search
0119  *  order for ioctls is (1) tty layer, (2) tty low-level driver, (3) line
0120  *  discpline. So a low-level driver can "grab" an ioctl request before
0121  *  the line discpline has a chance to see it.
0122  *
0123  * @compat_ioctl: [TTY] ``int ()(struct tty_struct *tty, unsigned int cmd,
0124  *      unsigned long arg)``
0125  *
0126  *  Process ioctl calls from 32-bit process on 64-bit system.
0127  *
0128  *  Note that only ioctls that are neither "pointer to compatible
0129  *  structure" nor tty-generic.  Something private that takes an integer or
0130  *  a pointer to wordsize-sensitive structure belongs here, but most of
0131  *  ldiscs will happily leave it %NULL.
0132  *
0133  * @set_termios: [TTY] ``void ()(struct tty_struct *tty, struct ktermios *old)``
0134  *
0135  *  This function notifies the line discpline that a change has been made
0136  *  to the termios structure.
0137  *
0138  * @poll: [TTY] ``int ()(struct tty_struct *tty, struct file *file,
0139  *        struct poll_table_struct *wait)``
0140  *
0141  *  This function is called when a user attempts to select/poll on a @tty
0142  *  device. It is solely the responsibility of the line discipline to
0143  *  handle poll requests.
0144  *
0145  * @hangup: [TTY] ``void ()(struct tty_struct *tty)``
0146  *
0147  *  Called on a hangup. Tells the discipline that it should cease I/O to
0148  *  the tty driver. The driver should seek to perform this action quickly
0149  *  but should wait until any pending driver I/O is completed. No further
0150  *  calls into the ldisc code will occur.
0151  *
0152  *  Can sleep.
0153  *
0154  * @receive_buf: [DRV] ``void ()(struct tty_struct *tty,
0155  *             const unsigned char *cp, const char *fp, int count)``
0156  *
0157  *  This function is called by the low-level tty driver to send characters
0158  *  received by the hardware to the line discpline for processing. @cp is
0159  *  a pointer to the buffer of input character received by the device. @fp
0160  *  is a pointer to an array of flag bytes which indicate whether a
0161  *  character was received with a parity error, etc. @fp may be %NULL to
0162  *  indicate all data received is %TTY_NORMAL.
0163  *
0164  * @write_wakeup: [DRV] ``void ()(struct tty_struct *tty)``
0165  *
0166  *  This function is called by the low-level tty driver to signal that line
0167  *  discpline should try to send more characters to the low-level driver
0168  *  for transmission. If the line discpline does not have any more data to
0169  *  send, it can just return. If the line discipline does have some data to
0170  *  send, please arise a tasklet or workqueue to do the real data transfer.
0171  *  Do not send data in this hook, it may lead to a deadlock.
0172  *
0173  * @dcd_change: [DRV] ``void ()(struct tty_struct *tty, unsigned int status)``
0174  *
0175  *  Tells the discipline that the DCD pin has changed its status. Used
0176  *  exclusively by the %N_PPS (Pulse-Per-Second) line discipline.
0177  *
0178  * @receive_buf2: [DRV] ``int ()(struct tty_struct *tty,
0179  *          const unsigned char *cp, const char *fp, int count)``
0180  *
0181  *  This function is called by the low-level tty driver to send characters
0182  *  received by the hardware to the line discpline for processing. @cp is a
0183  *  pointer to the buffer of input character received by the device.  @fp
0184  *  is a pointer to an array of flag bytes which indicate whether a
0185  *  character was received with a parity error, etc. @fp may be %NULL to
0186  *  indicate all data received is %TTY_NORMAL. If assigned, prefer this
0187  *  function for automatic flow control.
0188  *
0189  * @lookahead_buf: [DRV] ``void ()(struct tty_struct *tty,
0190  *          const unsigned char *cp, const char *fp, int count)``
0191  *
0192  *  This function is called by the low-level tty driver for characters
0193  *  not eaten by ->receive_buf() or ->receive_buf2(). It is useful for
0194  *  processing high-priority characters such as software flow-control
0195  *  characters that could otherwise get stuck into the intermediate
0196  *  buffer until tty has room to receive them. Ldisc must be able to
0197  *  handle later a ->receive_buf() or ->receive_buf2() call for the
0198  *  same characters (e.g. by skipping the actions for high-priority
0199  *  characters already handled by ->lookahead_buf()).
0200  *
0201  * @owner: module containting this ldisc (for reference counting)
0202  *
0203  * This structure defines the interface between the tty line discipline
0204  * implementation and the tty routines. The above routines can be defined.
0205  * Unless noted otherwise, they are optional, and can be filled in with a %NULL
0206  * pointer.
0207  *
0208  * Hooks marked [TTY] are invoked from the TTY core, the [DRV] ones from the
0209  * tty_driver side.
0210  */
0211 struct tty_ldisc_ops {
0212     char    *name;
0213     int num;
0214
0215     /*
0216      * The following routines are called from above.
0217      */
0218     int (*open)(struct tty_struct *tty);
0219     void    (*close)(struct tty_struct *tty);
0220     void    (*flush_buffer)(struct tty_struct *tty);
0221     ssize_t (*read)(struct tty_struct *tty, struct file *file,
0222             unsigned char *buf, size_t nr,
0223             void **cookie, unsigned long offset);
0224     ssize_t (*write)(struct tty_struct *tty, struct file *file,
0225              const unsigned char *buf, size_t nr);
0226     int (*ioctl)(struct tty_struct *tty, unsigned int cmd,
0227             unsigned long arg);
0228     int (*compat_ioctl)(struct tty_struct *tty, unsigned int cmd,
0229             unsigned long arg);
0230     void    (*set_termios)(struct tty_struct *tty, struct ktermios *old);
0231     __poll_t (*poll)(struct tty_struct *tty, struct file *file,
0232                  struct poll_table_struct *wait);
0233     void    (*hangup)(struct tty_struct *tty);
0234
0235     /*
0236      * The following routines are called from below.
0237      */
0238     void    (*receive_buf)(struct tty_struct *tty, const unsigned char *cp,
0239                    const char *fp, int count);
0240     void    (*write_wakeup)(struct tty_struct *tty);
0241     void    (*dcd_change)(struct tty_struct *tty, unsigned int status);
0242     int (*receive_buf2)(struct tty_struct *tty, const unsigned char *cp,
0243                 const char *fp, int count);
0244     void    (*lookahead_buf)(struct tty_struct *tty, const unsigned char *cp,
0245                  const unsigned char *fp, unsigned int count);
0246
0247     struct  module *owner;
0248 };
0249
0250 struct tty_ldisc {
0251     struct tty_ldisc_ops *ops;
0252     struct tty_struct *tty;
0253 };
0254
0255 #define MODULE_ALIAS_LDISC(ldisc) \
0256     MODULE_ALIAS("tty-ldisc-" __stringify(ldisc))
0257
0258 extern const struct seq_operations tty_ldiscs_seq_ops;
0259
0260 struct tty_ldisc *tty_ldisc_ref(struct tty_struct *);
0261 void tty_ldisc_deref(struct tty_ldisc *);
0262 struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *);
0263
0264 void tty_ldisc_flush(struct tty_struct *tty);
0265
0266 int tty_register_ldisc(struct tty_ldisc_ops *new_ldisc);
0267 void tty_unregister_ldisc(struct tty_ldisc_ops *ldisc);
0268 int tty_set_ldisc(struct tty_struct *tty, int disc);
0269
0270 #endif /* _LINUX_TTY_LDISC_H */