[linux-lvm] snapshot of Reiserfs
Chris Mason
mason at suse.com
Wed Feb 21 19:17:27 UTC 2001
On Wednesday, February 21, 2001 11:55:14 AM -0700 Andreas Dilger
<adilger at turbolinux.com> wrote:
>> > Given that the VFS support for the *unlockfs methods is included in
>> > 2.4.1, this should probably become something like:
>> >
>> > /* lvm_do_lv_create calls fsync_dev_lockfs()/unlockfs() */
>> > #if LINUX_KERNEL_VERSION >= KERNEL_VERSION(2,4,1)
>> > #define LVM_VFS_ENHANCEMENT
>> > #else
>> > /* Need to apply a kernel patch to add lockfs/unlockfs VFS methods */
>> > /* #define LVM_VFS_ENHANCEMENT */
>> > #endif
>> >
>>
>> I like this idea.
>
> Note that I thought the fsync_dev_lockfs() code was added to 2.4.1 when
> reiserfs was added. However, it appears that only the *lockfs pointers
> were added to the super_operations, and the actual code that uses them
> was NOT added. This means we can't do the above until fsync_dev_lockfs()
> is actually there.
>
Yes, it would have been smarter for me to push for the entire lockfs patch
a long time ago.
>> > Also, if the sync_supers_lockfs() method is changed to call
>> > write_super() if write_super_lockfs() doesn't exist, like:
>>
>> The fsync_dev_lockfs call does this for us, if there is no
>> write_super_lockfs provided, fsync_dev_lockfs is effectively the same as
>> calling fsync_dev.
>
> Except that fsync_dev() calls the write_super() method, and
> fsync_dev_lockfs() only calls the write_super_lockfs() method if it
> exists - it does not call write_super() if write_super_lockfs() does not
> exist. If it were changed as I suggest, then the two would be the same.
Hmmm, fsync_dev_lockfs should look like this:
+int fsync_dev_lockfs(kdev_t dev)
+{
+ sync_buffers(dev, 0);
+
+ lock_kernel();
+ sync_supers(dev);
^^^^^^^^^^^^^^^^^^
+ /* note, the FS might need to start transactions to
+ ** sync the inodes, or the quota, no locking until
+ ** after these are done
+ */
+ sync_inodes(dev);
+ DQUOT_SYNC(dev);
+ /* if inodes or quotas could be dirtied during the
+ ** sync_supers_lockfs call, the FS is responsible for getting
+ ** them on disk, without deadlocking against the lock
+ */
+ sync_supers_lockfs(dev) ;
+ unlock_kernel();
+
+ return sync_buffers(dev, 1) ;
+}
+
It is amost exactly a cut n' paste of fsync_dev, with an extra call to
sync_supers_lockfs. It should do what fsync_dev does, even when there are
no sync_super_lockfs methods are provided. The only reason I didn't just
call fsync_dev from fsync_dev_lockfs is because I wanted the sync_buffers
call to happen after the lockfs call ;-)
-chris
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