Messages in this thread | | | Date | Tue, 26 Mar 2013 13:55:30 +0400 | From | "Maxim V. Patlasov" <> | Subject | Re: [PATCH 07/14] fuse: Update i_mtime on buffered writes |
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Hi Miklos,
Sorry for long delay, see please inline comment below.
01/30/2013 02:19 AM, Miklos Szeredi пишет: > On Fri, Jan 25, 2013 at 7:24 PM, Maxim V. Patlasov > <MPatlasov@parallels.com> wrote: >> If writeback cache is on, buffered write doesn't result in immediate mtime >> update in userspace because the userspace will see modified data later, when >> writeback happens. Consequently, mtime provided by userspace may be older than >> actual time of buffered write. >> >> The problem can be solved by generating mtime locally (will come in next >> patches) and flushing it to userspace periodically. Here we introduce a flag to >> keep the state of fuse_inode: the flag is ON if and only if locally generated >> mtime (stored in inode->i_mtime) was not pushed to the userspace yet. >> >> The patch also implements all bits related to flushing and clearing the flag. >> >> Signed-off-by: Maxim Patlasov <MPatlasov@parallels.com> >> --- >> fs/fuse/dir.c | 42 +++++++++++++++++++++++++---- >> fs/fuse/file.c | 31 ++++++++++++++++++--- >> fs/fuse/fuse_i.h | 13 ++++++++- >> fs/fuse/inode.c | 79 +++++++++++++++++++++++++++++++++++++++++++++++++++++- >> 4 files changed, 154 insertions(+), 11 deletions(-) >> >> diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c >> index ff8b603..969c60d 100644 >> --- a/fs/fuse/dir.c >> +++ b/fs/fuse/dir.c >> @@ -177,6 +177,13 @@ static int fuse_dentry_revalidate(struct dentry *entry, unsigned int flags) >> if (flags & LOOKUP_RCU) >> return -ECHILD; >> >> + if (test_bit(FUSE_I_MTIME_UPDATED, >> + &get_fuse_inode(inode)->state)) { >> + err = fuse_flush_mtime(inode, 0); > ->d_revalidate may be called with or without i_mutex, there's > absolutely no way to know. So this won't work. > > I know it was me who suggested this approach, but I have second > thoughts... I really don't like the way this mixes userspace and > kernel updates to mtime. I think it should be either one or the > other. > > I don't think you need to much changes to this patch. Just clear > S_NOCMTIME, implement i_op->update_time(), which sets the > FUSE_I_MTIME_UPDATED flag and flush mtime just like you do now. > Except now it doesn't need to take i_mutex since all mtime updates are > now done by the kernel. > > Does that make sense?
Yes, but it's not as simple as you described above. mtime updates should be strictly serialized, I used i_mutex for this purpose. Abandoning i_mutex, we'll have to introduce another lock for synchronization. Otherwise, we won't know when it's secure to clear FUSE_I_MTIME_UPDATED flag. Another approach is to introduce one more state: FUSE_I_MTIME_UPDATE_IN_PROGRESS. But again, we'll need something like waitq to wait for mtime update completion.
I'd prefer much more simple solution: clear S_NOCMTIME and implement i_op->update_time() as you suggested; but flush mtime only on last close. May be we could extend FUSE_RELEASE request (struct fuse_release_in) to accommodate mtime. Are you OK about it?
Thanks, Maxim
> > Thanks, > Miklos >
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