v4.19.13 snapshot.
diff --git a/include/linux/tty_ldisc.h b/include/linux/tty_ldisc.h
new file mode 100644
index 0000000..840894c
--- /dev/null
+++ b/include/linux/tty_ldisc.h
@@ -0,0 +1,221 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_TTY_LDISC_H
+#define _LINUX_TTY_LDISC_H
+
+/*
+ * This structure defines the interface between the tty line discipline
+ * implementation and the tty routines. The following routines can be
+ * defined; unless noted otherwise, they are optional, and can be
+ * filled in with a null pointer.
+ *
+ * int (*open)(struct tty_struct *);
+ *
+ * This function is called when the line discipline is associated
+ * with the tty. The line discipline can use this as an
+ * opportunity to initialize any state needed by the ldisc routines.
+ *
+ * void (*close)(struct tty_struct *);
+ *
+ * This function is called when the line discipline is being
+ * shutdown, either because the tty is being closed or because
+ * the tty is being changed to use a new line discipline
+ *
+ * void (*flush_buffer)(struct tty_struct *tty);
+ *
+ * This function instructs the line discipline to clear its
+ * buffers of any input characters it may have queued to be
+ * delivered to the user mode process.
+ *
+ * ssize_t (*read)(struct tty_struct * tty, struct file * file,
+ * unsigned char * buf, size_t nr);
+ *
+ * This function is called when the user requests to read from
+ * the tty. The line discipline will return whatever characters
+ * it has buffered up for the user. If this function is not
+ * defined, the user will receive an EIO error.
+ *
+ * ssize_t (*write)(struct tty_struct * tty, struct file * file,
+ * const unsigned char * buf, size_t nr);
+ *
+ * This function is called when the user requests to write to the
+ * tty. The line discipline will deliver the characters to the
+ * low-level tty device for transmission, optionally performing
+ * some processing on the characters first. If this function is
+ * not defined, the user will receive an EIO error.
+ *
+ * int (*ioctl)(struct tty_struct * tty, struct file * file,
+ * unsigned int cmd, unsigned long arg);
+ *
+ * This function is called when the user requests an ioctl which
+ * is not handled by the tty layer or the low-level tty driver.
+ * It is intended for ioctls which affect line discpline
+ * operation. Note that the search order for ioctls is (1) tty
+ * layer, (2) tty low-level driver, (3) line discpline. So a
+ * low-level driver can "grab" an ioctl request before the line
+ * discpline has a chance to see it.
+ *
+ * long (*compat_ioctl)(struct tty_struct * tty, struct file * file,
+ * unsigned int cmd, unsigned long arg);
+ *
+ * Process ioctl calls from 32-bit process on 64-bit system
+ *
+ * void (*set_termios)(struct tty_struct *tty, struct ktermios * old);
+ *
+ * This function notifies the line discpline that a change has
+ * been made to the termios structure.
+ *
+ * int (*poll)(struct tty_struct * tty, struct file * file,
+ * poll_table *wait);
+ *
+ * This function is called when a user attempts to select/poll on a
+ * tty device. It is solely the responsibility of the line
+ * discipline to handle poll requests.
+ *
+ * void (*receive_buf)(struct tty_struct *, const unsigned char *cp,
+ * char *fp, int count);
+ *
+ * This function is called by the low-level tty driver to send
+ * characters received by the hardware to the line discpline for
+ * processing. <cp> is a pointer to the buffer of input
+ * character received by the device. <fp> is a pointer to a
+ * pointer of flag bytes which indicate whether a character was
+ * received with a parity error, etc. <fp> may be NULL to indicate
+ * all data received is TTY_NORMAL.
+ *
+ * void (*write_wakeup)(struct tty_struct *);
+ *
+ * This function is called by the low-level tty driver to signal
+ * that line discpline should try to send more characters to the
+ * low-level driver for transmission. If the line discpline does
+ * not have any more data to send, it can just return. If the line
+ * discipline does have some data to send, please arise a tasklet
+ * or workqueue to do the real data transfer. Do not send data in
+ * this hook, it may leads to a deadlock.
+ *
+ * int (*hangup)(struct tty_struct *)
+ *
+ * Called on a hangup. Tells the discipline that it should
+ * cease I/O to the tty driver. Can sleep. The driver should
+ * seek to perform this action quickly but should wait until
+ * any pending driver I/O is completed.
+ *
+ * void (*dcd_change)(struct tty_struct *tty, unsigned int status)
+ *
+ * Tells the discipline that the DCD pin has changed its status.
+ * Used exclusively by the N_PPS (Pulse-Per-Second) line discipline.
+ *
+ * int (*receive_buf2)(struct tty_struct *, const unsigned char *cp,
+ * char *fp, int count);
+ *
+ * This function is called by the low-level tty driver to send
+ * characters received by the hardware to the line discpline for
+ * processing. <cp> is a pointer to the buffer of input
+ * character received by the device. <fp> is a pointer to a
+ * pointer of flag bytes which indicate whether a character was
+ * received with a parity error, etc. <fp> may be NULL to indicate
+ * all data received is TTY_NORMAL.
+ * If assigned, prefer this function for automatic flow control.
+ */
+
+#include <linux/fs.h>
+#include <linux/wait.h>
+#include <linux/atomic.h>
+
+/*
+ * the semaphore definition
+ */
+struct ld_semaphore {
+ atomic_long_t count;
+ raw_spinlock_t wait_lock;
+ unsigned int wait_readers;
+ struct list_head read_wait;
+ struct list_head write_wait;
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+ struct lockdep_map dep_map;
+#endif
+};
+
+extern void __init_ldsem(struct ld_semaphore *sem, const char *name,
+ struct lock_class_key *key);
+
+#define init_ldsem(sem) \
+do { \
+ static struct lock_class_key __key; \
+ \
+ __init_ldsem((sem), #sem, &__key); \
+} while (0)
+
+
+extern int ldsem_down_read(struct ld_semaphore *sem, long timeout);
+extern int ldsem_down_read_trylock(struct ld_semaphore *sem);
+extern int ldsem_down_write(struct ld_semaphore *sem, long timeout);
+extern int ldsem_down_write_trylock(struct ld_semaphore *sem);
+extern void ldsem_up_read(struct ld_semaphore *sem);
+extern void ldsem_up_write(struct ld_semaphore *sem);
+
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+extern int ldsem_down_read_nested(struct ld_semaphore *sem, int subclass,
+ long timeout);
+extern int ldsem_down_write_nested(struct ld_semaphore *sem, int subclass,
+ long timeout);
+#else
+# define ldsem_down_read_nested(sem, subclass, timeout) \
+ ldsem_down_read(sem, timeout)
+# define ldsem_down_write_nested(sem, subclass, timeout) \
+ ldsem_down_write(sem, timeout)
+#endif
+
+
+struct tty_ldisc_ops {
+ int magic;
+ char *name;
+ int num;
+ int flags;
+
+ /*
+ * The following routines are called from above.
+ */
+ int (*open)(struct tty_struct *);
+ void (*close)(struct tty_struct *);
+ void (*flush_buffer)(struct tty_struct *tty);
+ ssize_t (*read)(struct tty_struct *tty, struct file *file,
+ unsigned char __user *buf, size_t nr);
+ ssize_t (*write)(struct tty_struct *tty, struct file *file,
+ const unsigned char *buf, size_t nr);
+ int (*ioctl)(struct tty_struct *tty, struct file *file,
+ unsigned int cmd, unsigned long arg);
+ long (*compat_ioctl)(struct tty_struct *tty, struct file *file,
+ unsigned int cmd, unsigned long arg);
+ void (*set_termios)(struct tty_struct *tty, struct ktermios *old);
+ __poll_t (*poll)(struct tty_struct *, struct file *,
+ struct poll_table_struct *);
+ int (*hangup)(struct tty_struct *tty);
+
+ /*
+ * The following routines are called from below.
+ */
+ void (*receive_buf)(struct tty_struct *, const unsigned char *cp,
+ char *fp, int count);
+ void (*write_wakeup)(struct tty_struct *);
+ void (*dcd_change)(struct tty_struct *, unsigned int);
+ int (*receive_buf2)(struct tty_struct *, const unsigned char *cp,
+ char *fp, int count);
+
+ struct module *owner;
+
+ int refcount;
+};
+
+struct tty_ldisc {
+ struct tty_ldisc_ops *ops;
+ struct tty_struct *tty;
+};
+
+#define TTY_LDISC_MAGIC 0x5403
+
+#define LDISC_FLAG_DEFINED 0x00000001
+
+#define MODULE_ALIAS_LDISC(ldisc) \
+ MODULE_ALIAS("tty-ldisc-" __stringify(ldisc))
+
+#endif /* _LINUX_TTY_LDISC_H */