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Subject[PATCH 1/4] devpts: Remove CONFIG_DEVPTS_MULTIPLE_INSTANCES

This compile option just makes the code more complicated and makes
it more difficult to transition to a time when we take advantage
of the new features that DEVPTS_MULTIPLE_INSTANCES allows.

Acked-by: "Serge E. Hallyn" <serge@hallyn.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
Documentation/filesystems/devpts.txt | 36 ++++++++++++---------------------
drivers/tty/Kconfig | 11 ----------
fs/devpts/inode.c | 28 --------------------------
3 files changed, 13 insertions(+), 62 deletions(-)
diff --git a/Documentation/filesystems/devpts.txt b/Documentation/filesystems/devpts.txt
index 68dffd8..260cf6d 100644
--- a/Documentation/filesystems/devpts.txt
+++ b/Documentation/filesystems/devpts.txt
@@ -6,33 +6,23 @@ allocated in other instances of devpts.
To preserve backward compatibility, this support for multiple instances is
enabled only if:

- - CONFIG_DEVPTS_MULTIPLE_INSTANCES=y, and
- '-o newinstance' mount option is specified while mounting devpts

IOW, devpts now supports both single-instance and multi-instance semantics.

-If CONFIG_DEVPTS_MULTIPLE_INSTANCES=n, there is no change in behavior and
-this referred to as the "legacy" mode. In this mode, the new mount options
-(-o newinstance and -o ptmxmode) will be ignored with a 'bogus option' message
-on console.
-
-If CONFIG_DEVPTS_MULTIPLE_INSTANCES=y and devpts is mounted without the
-'newinstance' option (as in current start-up scripts) the new mount binds
-to the initial kernel mount of devpts. This mode is referred to as the
-'single-instance' mode and the current, single-instance semantics are
-preserved, i.e PTYs are common across the system.
-
-The only difference between this single-instance mode and the legacy mode
-is the presence of new, '/dev/pts/ptmx' node with permissions 0000, which
-can safely be ignored.
-
-If CONFIG_DEVPTS_MULTIPLE_INSTANCES=y and 'newinstance' option is specified,
-the mount is considered to be in the multi-instance mode and a new instance
-of the devpts fs is created. Any ptys created in this instance are independent
-of ptys in other instances of devpts. Like in the single-instance mode, the
-/dev/pts/ptmx node is present. To effectively use the multi-instance mode,
-open of /dev/ptmx must be a redirected to '/dev/pts/ptmx' using a symlink or
-bind-mount.
+If devpts is mounted without the 'newinstance' option (as in current
+start-up scripts) the new mount binds to the initial kernel mount of
+devpts. This mode is referred to as the 'single-instance' mode and the
+current, single-instance semantics are preserved, i.e PTYs are common
+across the system.
+
+If 'newinstance' option is specified, the mount is considered to be in
+the multi-instance mode and a new instance of the devpts fs is
+created. Any ptys created in this instance are independent of ptys in
+other instances of devpts. Like in the single-instance mode, the
+/dev/pts/ptmx node is present. To effectively use the multi-instance
+mode, open of /dev/ptmx must be a redirected to '/dev/pts/ptmx' using
+a symlink or bind-mount.

Eg: A container startup script could do the following:

diff --git a/drivers/tty/Kconfig b/drivers/tty/Kconfig
index 830cd62..5e5cd3e 100644
--- a/drivers/tty/Kconfig
+++ b/drivers/tty/Kconfig
@@ -109,17 +109,6 @@ config UNIX98_PTYS
All modern Linux systems use the Unix98 ptys. Say Y unless
you're on an embedded system and want to conserve memory.

-config DEVPTS_MULTIPLE_INSTANCES
- bool "Support multiple instances of devpts"
- depends on UNIX98_PTYS
- default n
- ---help---
- Enable support for multiple instances of devpts filesystem.
- If you want to have isolated PTY namespaces (eg: in containers),
- say Y here. Otherwise, say N. If enabled, each mount of devpts
- filesystem with the '-o newinstance' option will create an
- independent PTY namespace.
-
config LEGACY_PTYS
bool "Legacy (BSD) PTY support"
default y
diff --git a/fs/devpts/inode.c b/fs/devpts/inode.c
index 14afbab..5f0d64e 100644
--- a/fs/devpts/inode.c
+++ b/fs/devpts/inode.c
@@ -115,11 +115,9 @@ static const match_table_t tokens = {
{Opt_uid, "uid=%u"},
{Opt_gid, "gid=%u"},
{Opt_mode, "mode=%o"},
-#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
{Opt_ptmxmode, "ptmxmode=%o"},
{Opt_newinstance, "newinstance"},
{Opt_max, "max=%d"},
-#endif
{Opt_err, NULL}
};

@@ -136,10 +134,8 @@ static inline struct pts_fs_info *DEVPTS_SB(struct super_block *sb)

static inline struct super_block *pts_sb_from_inode(struct inode *inode)
{
-#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
if (inode->i_sb->s_magic == DEVPTS_SUPER_MAGIC)
return inode->i_sb;
-#endif
return devpts_mnt->mnt_sb;
}

@@ -206,7 +202,6 @@ static int parse_mount_options(char *data, int op, struct pts_mount_opts *opts)
return -EINVAL;
opts->mode = option & S_IALLUGO;
break;
-#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
case Opt_ptmxmode:
if (match_octal(&args[0], &option))
return -EINVAL;
@@ -223,7 +218,6 @@ static int parse_mount_options(char *data, int op, struct pts_mount_opts *opts)
return -EINVAL;
opts->max = option;
break;
-#endif
default:
printk(KERN_ERR "devpts: called with bogus options\n");
return -EINVAL;
@@ -233,7 +227,6 @@ static int parse_mount_options(char *data, int op, struct pts_mount_opts *opts)
return 0;
}

-#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
static int mknod_ptmx(struct super_block *sb)
{
int mode;
@@ -291,12 +284,6 @@ static void update_ptmx_mode(struct pts_fs_info *fsi)
inode->i_mode = S_IFCHR|fsi->mount_opts.ptmxmode;
}
}
-#else
-static inline void update_ptmx_mode(struct pts_fs_info *fsi)
-{
- return;
-}
-#endif

static int devpts_remount(struct super_block *sb, int *flags, char *data)
{
@@ -327,11 +314,9 @@ static int devpts_show_options(struct seq_file *seq, struct dentry *root)
if (opts->setgid)
seq_printf(seq, ",gid=%u", from_kgid_munged(&init_user_ns, opts->gid));
seq_printf(seq, ",mode=%03o", opts->mode);
-#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
seq_printf(seq, ",ptmxmode=%03o", opts->ptmxmode);
if (opts->max < NR_UNIX98_PTY_MAX)
seq_printf(seq, ",max=%d", opts->max);
-#endif

return 0;
}
@@ -392,7 +377,6 @@ fail:
return -ENOMEM;
}

-#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
static int compare_init_pts_sb(struct super_block *s, void *p)
{
if (devpts_mnt)
@@ -467,18 +451,6 @@ out_undo_sget:
return ERR_PTR(error);
}

-#else
-/*
- * This supports only the legacy single-instance semantics (no
- * multiple-instance semantics)
- */
-static struct dentry *devpts_mount(struct file_system_type *fs_type, int flags,
- const char *dev_name, void *data)
-{
- return mount_single(fs_type, flags, data, devpts_fill_super);
-}
-#endif
-
static void devpts_kill_sb(struct super_block *sb)
{
struct pts_fs_info *fsi = DEVPTS_SB(sb);
--
1.7.5.4


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