add new system file

hc

2024-02-20 102a0743326a03cd1a1202ceda21e175b7d3575c

 kernel/drivers/tty/tty_ldisc.c
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@@ -19,6 +19,7 @@
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 #include <linux/seq_file.h>
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 #include <linux/uaccess.h>
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 #include <linux/ratelimit.h>
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+#include "tty.h"
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 #undef LDISC_DEBUG_HANGUP
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@@ -79,7 +80,6 @@
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 /**
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  *	tty_unregister_ldisc	-	unload a line discipline
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  *	@disc: ldisc number
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- *	@new_ldisc: pointer to the ldisc object
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  *
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  *	Remove a line discipline from the kernel providing it is not
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  *	currently in use.
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@@ -156,12 +156,7 @@
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  *		takes tty_ldiscs_lock to guard against ldisc races
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  */
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-#if defined(CONFIG_LDISC_AUTOLOAD)
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-	#define INITIAL_AUTOLOAD_STATE	1
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-#else
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-	#define INITIAL_AUTOLOAD_STATE	0
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-#endif
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-static int tty_ldisc_autoload = INITIAL_AUTOLOAD_STATE;
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+static int tty_ldisc_autoload = IS_BUILTIN(CONFIG_LDISC_AUTOLOAD);
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 static struct tty_ldisc *tty_ldisc_get(struct tty_struct *tty, int disc)
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 {
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@@ -487,6 +482,7 @@
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 static void tty_ldisc_close(struct tty_struct *tty, struct tty_ldisc *ld)
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 {
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+	lockdep_assert_held_write(&tty->ldisc_sem);
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 	WARN_ON(!test_bit(TTY_LDISC_OPEN, &tty->flags));
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 	clear_bit(TTY_LDISC_OPEN, &tty->flags);
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 	if (ld->ops->close)
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@@ -508,6 +504,7 @@
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 	struct tty_ldisc *disc = tty_ldisc_get(tty, ld);
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 	int r;
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+	lockdep_assert_held_write(&tty->ldisc_sem);
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 	if (IS_ERR(disc))
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 		return PTR_ERR(disc);
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 	tty->ldisc = disc;
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@@ -545,7 +542,7 @@
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 /**
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  *	tty_set_ldisc		-	set line discipline
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  *	@tty: the terminal to set
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- *	@ldisc: the line discipline
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+ *	@disc: the line discipline number
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  *
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  *	Set the discipline of a tty line. Must be called from a process
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  *	context. The ldisc change logic has to protect itself against any
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@@ -631,6 +628,7 @@
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  */
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 static void tty_ldisc_kill(struct tty_struct *tty)
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 {
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+	lockdep_assert_held_write(&tty->ldisc_sem);
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 	if (!tty->ldisc)
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 		return;
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 	/*
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@@ -678,6 +676,7 @@
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 	struct tty_ldisc *ld;
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 	int retval;
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+	lockdep_assert_held_write(&tty->ldisc_sem);
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 	ld = tty_ldisc_get(tty, disc);
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 	if (IS_ERR(ld)) {
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 		BUG_ON(disc == N_TTY);
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@@ -776,6 +775,10 @@
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 		return retval;
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 	if (o_tty) {
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+		/*
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+		 * Called without o_tty->ldisc_sem held, as o_tty has been
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+		 * just allocated and no one has a reference to it.
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+		 */
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 		retval = tty_ldisc_open(o_tty, o_tty->ldisc);
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 		if (retval) {
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 			tty_ldisc_close(tty, tty->ldisc);
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@@ -841,13 +844,12 @@
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  */
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 void tty_ldisc_deinit(struct tty_struct *tty)
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 {
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+	/* no ldisc_sem, tty is being destroyed */
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 	if (tty->ldisc)
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 		tty_ldisc_put(tty->ldisc);
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 	tty->ldisc = NULL;
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 }
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-static int zero;
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-static int one = 1;
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 static struct ctl_table tty_table[] = {
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 	{
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 		.procname	= "ldisc_autoload",
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@@ -855,8 +857,8 @@
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 		.maxlen		= sizeof(tty_ldisc_autoload),
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 		.mode		= 0644,
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 		.proc_handler	= proc_dointvec,
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-		.extra1		= &zero,
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-		.extra2		= &one,
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+		.extra1		= SYSCTL_ZERO,
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+		.extra2		= SYSCTL_ONE,
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 	},
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 	{ }
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 };