[PATCH 00/20] Mount writer count and read-only bind mounts (v3)
- From: Dave Hansen <haveblue@xxxxxxxxxx>
- Date: Tue, 27 Jun 2006 15:14:36 -0700
I think these are ready for -mm. They've gone through a few revisions
and a week or two of normal burn-in testing.
---
The following series implements read-only bind mounts. This feature
allows a read-only view into a read-write filesystem. In the process
of doing that, it also provides infrastructure for keeping track of
the number of writers to any given mount. New in this version is that
if that number is non-zero, remounts from r/w to r/o are not allowed.
This set does not take the previously tried approach of pushing down
the vfsmount structure deeply into call paths, such that it might be
checked in functions like permission(), may_create() and may_open().
Instead, it does checks near the entry points in the kernel, bumping
a reference count in the vfsmount structure. I've also eliminated
the use of the MNT_RDONLY flag. It was redundant since we have the
reference count.
This set also makes no attempt to keep the return codes for these
r/o bind mounts the same as for a real r/o filesystem or device.
It would require significantly more code and be quite a bit more
invasive. Unless there is a very strong reason to do so, I believe
it isn't worth the trouble.
One note: the previous patches all worked this way:
mount --bind -o ro /source /dest
These patches have changed that behavior. It now requires two steps:
mount --bind /source /dest
mount -o remount,ro /dest
Since the last revision, the locking in faccessat() and
mnt_is_readonly() has been changed to fix a race which might have
caused a false-negative mount-is-readonly return when faccessat()
is called while another two processes are racing to make a mount
readonly.
Signed-off-by: Dave Hansen <haveblue@xxxxxxxxxx>
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- Follow-Ups:
- Re: [PATCH 00/20] Mount writer count and read-only bind mounts (v3)
- From: Andrew Morton
- [PATCH 20/20] honor r/w changes at do_remount() time
- From: Dave Hansen
- [PATCH 14/20] elevate write count for do_utimes()
- From: Dave Hansen
- [PATCH 12/20] tricky: elevate write count files are open()ed
- From: Dave Hansen
- [PATCH 05/20] elevate write count during entire ncp_ioctl()
- From: Dave Hansen
- [PATCH 15/20] elevate write count for do_sys_utime() and touch_atime()
- From: Dave Hansen
- [PATCH 07/20] elevate mount count for extended attributes
- From: Dave Hansen
- [PATCH 02/20] r/o bind mount prepwork: move open_namei()'s vfs_create()
- From: Dave Hansen
- [PATCH 10/20] unix_find_other() elevate write count for touch_atime()
- From: Dave Hansen
- [PATCH 06/20] sys_symlinkat() elevate write count around vfs_symlink()
- From: Dave Hansen
- [PATCH 18/20] do_rmdir(): elevate write count
- From: Dave Hansen
- [PATCH 19/20] elevate writer count for custom 'struct file'
- From: Dave Hansen
- [PATCH 03/20] Add vfsmount writer count
- From: Dave Hansen
- [PATCH 09/20] mount_is_safe(): add comment
- From: Dave Hansen
- [PATCH 01/20] prepare for write access checks: collapse if()
- From: Dave Hansen
- [PATCH 13/20] elevate writer count for do_sys_truncate()
- From: Dave Hansen
- [PATCH 04/20] elevate mnt writers for callers of vfs_mkdir()
- From: Dave Hansen
- [PATCH 08/20] sys_linkat(): elevate write count around vfs_link()
- From: Dave Hansen
- [PATCH 16/20] sys_mknodat(): elevate write count for vfs_mknod/create()
- From: Dave Hansen
- [PATCH 17/20] elevate mnt writers for vfs_unlink() callers
- From: Dave Hansen
- [PATCH 11/20] elevate write count over calls to vfs_rename()
- From: Dave Hansen
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