Dave Hansen [EMAIL PROTECTED] wrote:
| On Fri, 2008-09-26 at 14:21 -0700, [EMAIL PROTECTED] wrote:
| > Dave Hansen [EMAIL PROTECTED] wrote:
| > | On Fri, 2008-09-12 at 10:53 -0700, [EMAIL PROTECTED] wrote:
| > | > + * But for single-mount semantics, devpts cannot use
get_sb_single(),
| > | > + * because get_sb_single()/sget() find and use the super-block from
| > | > + * 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.
| > |
| > | Can't you just override the test() function to get what you want here?
| >
| > get_sb_single() does not take a test() parameter and so I would still
| > need a get_sb_ref() or get_sb_special() interface right ?
| >
| > This special interface could call sget() with a custom-test function,
| > to get the super-block. But in case of devpts, we already have the
| > super-block. So we don't need to call sget(). We just need get a reference
| > and remount.
|
| Well, you shouldn't be using get_sb_single() at all any more, right?
How about something along these lines.
(applies on current devpts patchset. Touch tested on 2.6.27-rc6+ttydev-0918)
Suka
---
>From f021ad44e1b21bdc9f47c152830f40893fbaaf6a Mon Sep 17 00:00:00 2001
From: Sukadev Bhattiprolu <[EMAIL PROTECTED]>
Date: Sat, 27 Sep 2008 11:22:48 -0700
Subject: [PATCH] Define/use get_sb_specific()
See function header of get_sb_specific() for details of new interface.
TODO: This is a quick/dirty patch and needs to be properly integrated into
the patchset, by:
- replace patch that defines get_sb_ref() with a patch that
defines get_sb_specific()
- update patch that uses get_sb_ref() to use get_sb_specific()
- extract common code in get_sb_specific() and get_sb_single()
into a new function ?
---
fs/devpts/inode.c | 20 +++++++++------
fs/super.c | 67 +++++++++++++++++++++++++++++++++++++++++++++++++++-
include/linux/fs.h | 5 ++++
3 files changed, 83 insertions(+), 9 deletions(-)
diff --git a/fs/devpts/inode.c b/fs/devpts/inode.c
index c54b010..2f6bfb9 100644
--- a/fs/devpts/inode.c
+++ b/fs/devpts/inode.c
@@ -416,22 +416,26 @@ static int init_pts_mount(struct file_system_type
*fs_type, int flags,
void *data, struct vfsmount *mnt)
{
int err;
+ struct super_block *test_sb;
- if (!devpts_mnt) {
- err = get_sb_single(fs_type, flags, data, devpts_fill_super,
- mnt);
+ test_sb = NULL;
+ if (devpts_mnt)
+ test_sb = devpts_mnt->mnt_sb;
+ err = get_sb_specific(fs_type, flags, data, devpts_fill_super,
+ test_sb, mnt);
+ if (err)
+ return err;
+
+ if (!devpts_mnt) {
err = mknod_ptmx(mnt->mnt_sb);
if (err) {
dput(mnt->mnt_sb->s_root);
deactivate_super(mnt->mnt_sb);
- } else
- devpts_mnt = mnt;
-
- return err;
+ }
}
- return get_sb_ref(devpts_mnt->mnt_sb, flags, data, mnt);
+ return err;
}
static int devpts_get_sb(struct file_system_type *fs_type,
diff --git a/fs/super.c b/fs/super.c
index ba7059c..e766bac 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -882,9 +882,74 @@ int get_sb_single(struct file_system_type *fs_type,
}
EXPORT_SYMBOL(get_sb_single);
+
+static int compare_specific(struct super_block *s, void *test_sb)
+{
+ return s == test_sb;
+}
+
+/*
+ * int get_sb_specific(fs_type, flags, *data, fill_super, test_sb, mnt)
+ *
+ * If super_block @test_sb exists, get it and remount it Otherwise,
+ * allocate a new super-block and mount it.
+ *
+ * This interface is needed to support multiple mounts in devpts while
+ * preserving backward compatibility of the current 'single-mount'
+ * 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(),
+ * because get_sb_single()/sget() find and use the super-block from
+ * 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.
+ *
+ * TODO:
+ * Except for the sget() call and test_sb parameter, this
+ * function is identical to get_sb_single(). Extract common
+ * code to a separate function.
+ */
+
+ */
+int get_sb_specific(struct file_system_type *fs_type,
+ int flags, void *data,
+ int (*fill_super)(struct super_block *, void *, int),
+ struct super_block *test_sb,
+ struct vfsmount *mnt)
+{
+ struct super_block *s;
+ int error;
+
+ /*
+ * Unlike other get_sb_* functions, the 'data' used for comparison
+ * is different from the options data.
+ *
+ * We use set_anon_super() which ignores 'data' parameter, so
+ * 'test_sb' being different from 'data' should not matter ?
+ */
+ s = sget(fs_type, compare_specific, set_anon_super, test_sb);
+ if (IS_ERR(s))
+ return PTR_ERR(s);
+ if (!s->s_root) {
+ s->s_flags = flags;
+ error = fill_super(s, data, flags & MS_SILENT ? 1 : 0);
+ if (error) {
+ up_write(&s->s_umount);
+ deactivate_super(s);
+ return error;
+ }
+ s->s_flags |= MS_ACTIVE;
+ }
+ do_remount_sb(s, flags, data, 0);
+ return simple_set_mnt(mnt, s);
+}
+
+EXPORT_SYMBOL(get_sb_specific);
/*
* int get_sb_ref(struct super_block *sb, int flags, void *data,
- struct vfsmount *mnt)
+ * struct vfsmount *mnt)
*
* This interface is needed to support multiple mounts in devpts while
* preserving backward compatibility of the current 'single-mount'
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 3bda46d..72fdfd5 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1512,6 +1512,11 @@ extern int get_sb_single(struct file_system_type
*fs_type,
int flags, void *data,
int (*fill_super)(struct super_block *, void *, int),
struct vfsmount *mnt);
+extern int get_sb_specific(struct file_system_type *fs_type,
+ int flags, void *data,
+ int (*fill_super)(struct super_block *, void *, int),
+ struct super_block *test_sb,
+ struct vfsmount *mnt);
extern int get_sb_ref(struct super_block *sb, int flags, void *data,
struct vfsmount *mnt);
extern int get_sb_nodev(struct file_system_type *fs_type,
--
1.5.2.5
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