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Date: Sat, 3 Jan 2009 17:15:45 +0100
From: Christoph Hellwig <hch@....de>
To: Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
Cc: "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org
Subject: Re: devpts multiple instances feedback
This is a little untested patch to massage the mount code into about
how it should look like:
Index: linux-2.6/fs/devpts/inode.c
===================================================================
--- linux-2.6.orig/fs/devpts/inode.c 2009-01-03 16:52:22.823672077 +0100
+++ linux-2.6/fs/devpts/inode.c 2009-01-03 17:14:24.153711598 +0100
@@ -329,106 +329,6 @@ static int compare_init_pts_sb(struct su
}
/*
- * Safely parse the mount options in @data and update @opts.
- *
- * devpts ends up parsing options two times during mount, due to the
- * two modes of operation it supports. The first parse occurs in
- * devpts_get_sb() when determining the mode (single-instance or
- * multi-instance mode). The second parse happens in devpts_remount()
- * or new_pts_mount() depending on the mode.
- *
- * Parsing of options modifies the @data making subsequent parsing
- * incorrect. So make a local copy of @data and parse it.
- *
- * Return: 0 On success, -errno on error
- */
-static int safe_parse_mount_options(void *data, struct pts_mount_opts *opts)
-{
- int rc;
- void *datacp;
-
- if (!data)
- return 0;
-
- /* Use kstrdup() ? */
- datacp = kmalloc(PAGE_SIZE, GFP_KERNEL);
- if (!datacp)
- return -ENOMEM;
-
- memcpy(datacp, data, PAGE_SIZE);
- rc = parse_mount_options((char *)datacp, PARSE_MOUNT, opts);
- kfree(datacp);
-
- return rc;
-}
-
-/*
- * Mount a new (private) instance of devpts. PTYs created in this
- * instance are independent of the PTYs in other devpts instances.
- */
-static int new_pts_mount(struct file_system_type *fs_type, int flags,
- void *data, struct vfsmount *mnt)
-{
- int err;
- struct pts_fs_info *fsi;
- struct pts_mount_opts *opts;
-
- printk(KERN_NOTICE "devpts: newinstance mount\n");
-
- err = get_sb_nodev(fs_type, flags, data, devpts_fill_super, mnt);
- if (err)
- return err;
-
- fsi = DEVPTS_SB(mnt->mnt_sb);
- opts = &fsi->mount_opts;
-
- err = parse_mount_options(data, PARSE_MOUNT, opts);
- if (err)
- goto fail;
-
- err = mknod_ptmx(mnt->mnt_sb);
- if (err)
- goto fail;
-
- return 0;
-
-fail:
- dput(mnt->mnt_sb->s_root);
- deactivate_super(mnt->mnt_sb);
- return err;
-}
-
-/*
- * Check if 'newinstance' mount option was specified in @data.
- *
- * Return: -errno on error (eg: invalid mount options specified)
- * : 1 if 'newinstance' mount option was specified
- * : 0 if 'newinstance' mount option was NOT specified
- */
-static int is_new_instance_mount(void *data)
-{
- int rc;
- struct pts_mount_opts opts;
-
- if (!data)
- return 0;
-
- rc = safe_parse_mount_options(data, &opts);
- if (!rc)
- rc = opts.newinstance;
-
- return rc;
-}
-
-/*
- * get_init_pts_sb()
- *
- * This interface is needed to support multiple namespace semantics in
- * devpts while preserving backward compatibility of the current 'single-
- * namespace' semantics. i.e all mounts of devpts without the 'newinstance'
- * mount option should bind to the initial kernel mount, like
- * get_sb_single().
- *
* Mounts with 'newinstance' option create a new private namespace.
*
* But for single-mount semantics, devpts cannot use get_sb_single(),
@@ -436,20 +336,43 @@ static int is_new_instance_mount(void *d
* the most recent mount of devpts. But that recent mount may be a
* 'newinstance' mount and get_sb_single() would pick the newinstance
* super-block instead of the initial super-block.
- *
- * This interface is identical to get_sb_single() except that it
- * consistently selects the 'single-namespace' superblock even in the
- * presence of the private namespace (i.e 'newinstance') super-blocks.
*/
-static int get_init_pts_sb(struct file_system_type *fs_type, int flags,
- void *data, struct vfsmount *mnt)
+static int devpts_get_sb(struct file_system_type *fs_type, int flags,
+ const char *dev_name, void *data, struct vfsmount *mnt)
{
+ struct pts_mount_opts opts = { 0, };
struct super_block *s;
int error;
- s = sget(fs_type, compare_init_pts_sb, set_anon_super, NULL);
- if (IS_ERR(s))
- return PTR_ERR(s);
+ if (data) {
+ error = parse_mount_options(data, PARSE_MOUNT, &opts);
+ if (error)
+ return error;
+ }
+
+ if (opts.newinstance) {
+ /*
+ * Mount a new (private) instance of devpts. PTYs created
+ * in this instance are independent of the PTYs in other devpts
+ * instances.
+ */
+
+ printk(KERN_NOTICE "devpts: creating new instance\n");
+
+ s = sget(fs_type, NULL, set_anon_super, NULL);
+ if (IS_ERR(s))
+ return PTR_ERR(s);
+ } else {
+ /*
+ * Mount or remount the initial kernel mount of devpts.
+ *
+ * This type of mount maintains the legacy, single-instance
+ * semantics, while the kernel still allows multiple-instances.
+ */
+ s = sget(fs_type, compare_init_pts_sb, set_anon_super, NULL);
+ if (IS_ERR(s))
+ return PTR_ERR(s);
+ }
if (!s->s_root) {
s->s_flags = flags;
@@ -461,46 +384,26 @@ static int get_init_pts_sb(struct file_s
}
s->s_flags |= MS_ACTIVE;
}
- do_remount_sb(s, flags, data, 0);
- return simple_set_mnt(mnt, s);
-}
-
-/*
- * Mount or remount the initial kernel mount of devpts. This type of
- * mount maintains the legacy, single-instance semantics, while the
- * kernel still allows multiple-instances.
- */
-static int init_pts_mount(struct file_system_type *fs_type, int flags,
- void *data, struct vfsmount *mnt)
-{
- int err;
-
- err = get_init_pts_sb(fs_type, flags, data, mnt);
- if (err)
- return err;
-
- err = mknod_ptmx(mnt->mnt_sb);
- if (err) {
- dput(mnt->mnt_sb->s_root);
- deactivate_super(mnt->mnt_sb);
- }
-
- return err;
-}
-
-static int devpts_get_sb(struct file_system_type *fs_type,
- int flags, const char *dev_name, void *data, struct vfsmount *mnt)
-{
- int new;
- new = is_new_instance_mount(data);
- if (new < 0)
- return new;
+ /*
+ * Copy over mount options structure into the superblock.
+ */
+ memcpy(&DEVPTS_SB(mnt->mnt_sb)->mount_opts, &opts, sizeof(opts));
+
+ error = simple_set_mnt(mnt, s);
+ if (error)
+ return error;
+
+ error = mknod_ptmx(mnt->mnt_sb);
+ if (error)
+ goto out_dput;
- if (new)
- return new_pts_mount(fs_type, flags, data, mnt);
+ return 0;
- return init_pts_mount(fs_type, flags, data, mnt);
+ out_dput:
+ dput(mnt->mnt_sb->s_root);
+ deactivate_super(mnt->mnt_sb);
+ return error;
}
#else
/*
--
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