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SubjectRe: [PATCH]: Factor out PTY index allocation
Quoting sukadev@us.ibm.com (sukadev@us.ibm.com):
> We noticed this while working on pts namespaces and believe this might
> be an useful change even as we rework our pts/device namespace approach.
>
> ---
>
> From: Sukadev Bhattiprolu <sukadev@us.ibm.com>
> Subject: [PATCH]: Factor out PTY index allocation
>
> Factor out the code used to allocate/free a pts index into new interfaces,
> devpts_new_index() and devpts_kill_index(). This localizes the external
> data structures used in managing the pts indices.
>
> Signed-off-by: Sukadev Bhattiprolu <sukadev@us.ibm.com>
> Signed-off-by: Serge Hallyn<serue@us.ibm.com>
> Signed-off-by: Matt Helsley<matthltc@us.ibm.com>

No traces of devpts namespaces here, so I assume this should be
non-offensive and fine for inclusion.

thanks,
-serge

> ---
> drivers/char/tty_io.c | 40 ++++++----------------------------------
> fs/devpts/inode.c | 42 +++++++++++++++++++++++++++++++++++++++++-
> include/linux/devpts_fs.h | 4 ++++
> 3 files changed, 51 insertions(+), 35 deletions(-)
>
> Index: 2.6.25-rc8-mm2/include/linux/devpts_fs.h
> ===================================================================
> --- 2.6.25-rc8-mm2.orig/include/linux/devpts_fs.h 2008-01-26 09:49:16.000000000 -0800
> +++ 2.6.25-rc8-mm2/include/linux/devpts_fs.h 2008-04-16 09:51:15.000000000 -0700
> @@ -17,6 +17,8 @@
>
> #ifdef CONFIG_UNIX98_PTYS
>
> +int devpts_new_index(void);
> +void devpts_kill_index(int idx);
> int devpts_pty_new(struct tty_struct *tty); /* mknod in devpts */
> struct tty_struct *devpts_get_tty(int number); /* get tty structure */
> void devpts_pty_kill(int number); /* unlink */
> @@ -24,6 +26,8 @@ void devpts_pty_kill(int number); /* u
> #else
>
> /* Dummy stubs in the no-pty case */
> +static inline int devpts_new_index(void) { return -EINVAL; }
> +static inline void devpts_kill_index(int idx) { }
> static inline int devpts_pty_new(struct tty_struct *tty) { return -EINVAL; }
> static inline struct tty_struct *devpts_get_tty(int number) { return NULL; }
> static inline void devpts_pty_kill(int number) { }
> Index: 2.6.25-rc8-mm2/drivers/char/tty_io.c
> ===================================================================
> --- 2.6.25-rc8-mm2.orig/drivers/char/tty_io.c 2008-04-16 09:51:11.000000000 -0700
> +++ 2.6.25-rc8-mm2/drivers/char/tty_io.c 2008-04-16 09:51:15.000000000 -0700
> @@ -91,7 +91,6 @@
> #include <linux/module.h>
> #include <linux/smp_lock.h>
> #include <linux/device.h>
> -#include <linux/idr.h>
> #include <linux/wait.h>
> #include <linux/bitops.h>
> #include <linux/delay.h>
> @@ -137,9 +136,6 @@ EXPORT_SYMBOL(tty_mutex);
>
> #ifdef CONFIG_UNIX98_PTYS
> extern struct tty_driver *ptm_driver; /* Unix98 pty masters; for /dev/ptmx */
> -extern int pty_limit; /* Config limit on Unix98 ptys */
> -static DEFINE_IDR(allocated_ptys);
> -static DEFINE_MUTEX(allocated_ptys_lock);
> static int ptmx_open(struct inode *, struct file *);
> #endif
>
> @@ -2636,15 +2632,9 @@ static void release_dev(struct file *fil
> */
> release_tty(tty, idx);
>
> -#ifdef CONFIG_UNIX98_PTYS
> /* Make this pty number available for reallocation */
> - if (devpts) {
> - mutex_lock(&allocated_ptys_lock);
> - idr_remove(&allocated_ptys, idx);
> - mutex_unlock(&allocated_ptys_lock);
> - }
> -#endif
> -
> + if (devpts)
> + devpts_kill_index(idx);
> }
>
> /**
> @@ -2800,29 +2790,13 @@ static int ptmx_open(struct inode *inode
> struct tty_struct *tty;
> int retval;
> int index;
> - int idr_ret;
>
> nonseekable_open(inode, filp);
>
> /* find a device that is not in use. */
> - mutex_lock(&allocated_ptys_lock);
> - if (!idr_pre_get(&allocated_ptys, GFP_KERNEL)) {
> - mutex_unlock(&allocated_ptys_lock);
> - return -ENOMEM;
> - }
> - idr_ret = idr_get_new(&allocated_ptys, NULL, &index);
> - if (idr_ret < 0) {
> - mutex_unlock(&allocated_ptys_lock);
> - if (idr_ret == -EAGAIN)
> - return -ENOMEM;
> - return -EIO;
> - }
> - if (index >= pty_limit) {
> - idr_remove(&allocated_ptys, index);
> - mutex_unlock(&allocated_ptys_lock);
> - return -EIO;
> - }
> - mutex_unlock(&allocated_ptys_lock);
> + index = devpts_new_index();
> + if (index < 0)
> + return index;
>
> mutex_lock(&tty_mutex);
> retval = init_dev(ptm_driver, index, &tty);
> @@ -2847,9 +2821,7 @@ out1:
> release_dev(filp);
> return retval;
> out:
> - mutex_lock(&allocated_ptys_lock);
> - idr_remove(&allocated_ptys, index);
> - mutex_unlock(&allocated_ptys_lock);
> + devpts_kill_index(index);
> return retval;
> }
> #endif
> Index: 2.6.25-rc8-mm2/fs/devpts/inode.c
> ===================================================================
> --- 2.6.25-rc8-mm2.orig/fs/devpts/inode.c 2008-02-27 15:17:59.000000000 -0800
> +++ 2.6.25-rc8-mm2/fs/devpts/inode.c 2008-04-16 09:51:15.000000000 -0700
> @@ -17,6 +17,7 @@
> #include <linux/namei.h>
> #include <linux/mount.h>
> #include <linux/tty.h>
> +#include <linux/idr.h>
> #include <linux/devpts_fs.h>
> #include <linux/parser.h>
> #include <linux/fsnotify.h>
> @@ -26,6 +27,10 @@
>
> #define DEVPTS_DEFAULT_MODE 0600
>
> +extern int pty_limit; /* Config limit on Unix98 ptys */
> +static DEFINE_IDR(allocated_ptys);
> +static DECLARE_MUTEX(allocated_ptys_lock);
> +
> static struct vfsmount *devpts_mnt;
> static struct dentry *devpts_root;
>
> @@ -171,9 +176,44 @@ static struct dentry *get_node(int num)
> return lookup_one_len(s, root, sprintf(s, "%d", num));
> }
>
> +int devpts_new_index(void)
> +{
> + int index;
> + int idr_ret;
> +
> +retry:
> + if (!idr_pre_get(&allocated_ptys, GFP_KERNEL)) {
> + return -ENOMEM;
> + }
> +
> + down(&allocated_ptys_lock);
> + idr_ret = idr_get_new(&allocated_ptys, NULL, &index);
> + if (idr_ret < 0) {
> + up(&allocated_ptys_lock);
> + if (idr_ret == -EAGAIN)
> + goto retry;
> + return -EIO;
> + }
> +
> + if (index >= pty_limit) {
> + idr_remove(&allocated_ptys, index);
> + up(&allocated_ptys_lock);
> + return -EIO;
> + }
> + up(&allocated_ptys_lock);
> + return index;
> +}
> +
> +void devpts_kill_index(int idx)
> +{
> + down(&allocated_ptys_lock);
> + idr_remove(&allocated_ptys, idx);
> + up(&allocated_ptys_lock);
> +}
> +
> int devpts_pty_new(struct tty_struct *tty)
> {
> - int number = tty->index;
> + int number = tty->index; /* tty layer puts index from devpts_new_index() in here */
> struct tty_driver *driver = tty->driver;
> dev_t device = MKDEV(driver->major, driver->minor_start+number);
> struct dentry *dentry;


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