Re: [RFC PATCH v4 9/9] ovl: implement containerized syncfs for overlayfs

[Chengguang Xu <cgxu519@mykernel.net>]

 ---- 在 星期五, 2021-04-09 21:51:26 Miklos Szeredi <miklos@szeredi.hu> 撰写 ----
 > On Fri, Nov 13, 2020 at 7:57 AM Chengguang Xu <cgxu519@mykernel.net> wrote:
 > >
 > > Now overlayfs can only sync dirty inode during syncfs,
 > > so remove unnecessary sync_filesystem() on upper file
 > > system.
 > >
 > > Signed-off-by: Chengguang Xu <cgxu519@mykernel.net>
 > > ---
 > >  fs/overlayfs/super.c | 11 ++++++++---
 > >  1 file changed, 8 insertions(+), 3 deletions(-)
 > >
 > > diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
 > > index 982b3954b47c..58507f1cd583 100644
 > > --- a/fs/overlayfs/super.c
 > > +++ b/fs/overlayfs/super.c
 > > @@ -15,6 +15,8 @@
 > >  #include <linux/seq_file.h>
 > >  #include <linux/posix_acl_xattr.h>
 > >  #include <linux/exportfs.h>
 > > +#include <linux/blkdev.h>
 > > +#include <linux/writeback.h>
 > >  #include "overlayfs.h"
 > >
 > >  MODULE_AUTHOR("Miklos Szeredi <miklos@szeredi.hu>");
 > > @@ -270,8 +272,7 @@ static int ovl_sync_fs(struct super_block *sb, int wait)
 > >          * Not called for sync(2) call or an emergency sync (SB_I_SKIP_SYNC).
 > >          * All the super blocks will be iterated, including upper_sb.
 > >          *
 > > -        * If this is a syncfs(2) call, then we do need to call
 > > -        * sync_filesystem() on upper_sb, but enough if we do it when being
 > > +        * if this is a syncfs(2) call, it will be enough we do it when being
 > >          * called with wait == 1.
 > >          */
 > >         if (!wait)
 > > @@ -280,7 +281,11 @@ static int ovl_sync_fs(struct super_block *sb, int wait)
 > >         upper_sb = ovl_upper_mnt(ofs)->mnt_sb;
 > >
 > >         down_read(&upper_sb->s_umount);
 > > -       ret = sync_filesystem(upper_sb);
 > > +       wait_sb_inodes(upper_sb);
 > > +       if (upper_sb->s_op->sync_fs)
 > > +               ret = upper_sb->s_op->sync_fs(upper_sb, wait);
 > > +       if (!ret)
 > > +               ret = sync_blockdev(upper_sb->s_bdev);
 > 
 > Should this instead be __sync_blockdev(..., wait)?
 
I don't remember why we skipped the case of (wait == 0) here, just guess it's not worth
to export internal function __sync_blockdev() to modules, do you prefer to call __sync_blockdev()
and handle both nowait and wait cases?


Thanks,
Chengguang