linux-kernel - Re: [PATCH 6/6] fuse: add mount option to disable synchronous release

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Date:	Fri, 22 Aug 2014 16:09:27 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	Maxim Patlasov <MPatlasov@...allels.com>
Cc:	fuse-devel <fuse-devel@...ts.sourceforge.net>,
	Anand Avati <avati@...ster.org>,
	Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 6/6] fuse: add mount option to disable synchronous release

On Thu, Aug 21, 2014 at 6:09 PM, Maxim Patlasov <MPatlasov@...allels.com> wrote:
> Synchronous release ensures that kernel fuse reports to userspace exactly
> last fput(). However, nothing guarantees that last fput() will happen in the
> context of close(2). So userspace applications must be prepared to the
> situation when close(2) returned, but processing of FUSE_RELEASE is not
> completed by fuse daemon yet. To make testing such use cases easier, the
> patch introduces DISABLE_SYNC_RELEASE mount option which effectively mask out
> FOPEN_SYNC_RELEASE flag.

Why not make this an INIT flag?  Much easier to add support for in userspace.

Thanks,
Miklos

>
> Signed-off-by: Maxim Patlasov <mpatlasov@...allels.com>
> ---
> ---
>  fs/fuse/file.c   |    3 ++-
>  fs/fuse/fuse_i.h |    3 +++
>  fs/fuse/inode.c  |    8 ++++++++
>  3 files changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> index b92143a..ad3d357 100644
> --- a/fs/fuse/file.c
> +++ b/fs/fuse/file.c
> @@ -296,7 +296,8 @@ static void fuse_prepare_release(struct fuse_file *ff, int flags, int opcode)
>
>  static bool must_release_synchronously(struct fuse_file *ff)
>  {
> -       return ff->open_flags & FOPEN_SYNC_RELEASE;
> +       return ff->open_flags & FOPEN_SYNC_RELEASE &&
> +               !(ff->fc->flags & FUSE_DISABLE_SYNC_RELEASE);
>  }
>
>  void fuse_release_common(struct file *file, int opcode)
> diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
> index e8e47a6..c5e2fca 100644
> --- a/fs/fuse/fuse_i.h
> +++ b/fs/fuse/fuse_i.h
> @@ -44,6 +44,9 @@
>      doing the mount will be allowed to access the filesystem */
>  #define FUSE_ALLOW_OTHER         (1 << 1)
>
> +/** Disable synchronous release */
> +#define FUSE_DISABLE_SYNC_RELEASE (1 << 2)
> +
>  /** Number of page pointers embedded in fuse_req */
>  #define FUSE_REQ_INLINE_PAGES 1
>
> diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
> index 03246cd..86d47d0 100644
> --- a/fs/fuse/inode.c
> +++ b/fs/fuse/inode.c
> @@ -463,6 +463,7 @@ enum {
>         OPT_ALLOW_OTHER,
>         OPT_MAX_READ,
>         OPT_BLKSIZE,
> +       OPT_DISABLE_SYNC_RELEASE,
>         OPT_ERR
>  };
>
> @@ -475,6 +476,7 @@ static const match_table_t tokens = {
>         {OPT_ALLOW_OTHER,               "allow_other"},
>         {OPT_MAX_READ,                  "max_read=%u"},
>         {OPT_BLKSIZE,                   "blksize=%u"},
> +       {OPT_DISABLE_SYNC_RELEASE,      "disable_sync_release"},
>         {OPT_ERR,                       NULL}
>  };
>
> @@ -560,6 +562,10 @@ static int parse_fuse_opt(char *opt, struct fuse_mount_data *d, int is_bdev)
>                         d->blksize = value;
>                         break;
>
> +               case OPT_DISABLE_SYNC_RELEASE:
> +                       d->flags |= FUSE_DISABLE_SYNC_RELEASE;
> +                       break;
> +
>                 default:
>                         return 0;
>                 }
> @@ -583,6 +589,8 @@ static int fuse_show_options(struct seq_file *m, struct dentry *root)
>                 seq_puts(m, ",default_permissions");
>         if (fc->flags & FUSE_ALLOW_OTHER)
>                 seq_puts(m, ",allow_other");
> +       if (fc->flags & FUSE_DISABLE_SYNC_RELEASE)
> +               seq_puts(m, ",disable_sync_release");
>         if (fc->max_read != ~0)
>                 seq_printf(m, ",max_read=%u", fc->max_read);
>         if (sb->s_bdev && sb->s_blocksize != FUSE_DEFAULT_BLKSIZE)
>
--
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