Re: [RESEND4, PATCH 1/2] fuse: retrieve: cap requested size to negotiated max_write

From: Miklos Szeredi <miklos@szeredi.hu>
To: Kirill Smelkov <kirr@nexedi.com>
Cc: Miklos Szeredi <mszeredi@redhat.com>,
	Han-Wen Nienhuys <hanwen@google.com>,
	Jakob Unterwurzacher <jakobunt@gmail.com>,
	Kirill Tkhai <ktkhai@virtuozzo.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	fuse-devel <fuse-devel@lists.sourceforge.net>,
	stable <stable@vger.kernel.org>
Subject: Re: [RESEND4, PATCH 1/2] fuse: retrieve: cap requested size to negotiated max_write
Date: Wed, 24 Apr 2019 17:02:42 +0200	[thread overview]
Message-ID: <CAJfpegtX6p+j+kRuudZ=yVM9Tgj7x4mBaiGuDoDCrZoRvBOt9Q@mail.gmail.com> (raw)
In-Reply-To: <20190424142249.GA28070@deco.navytux.spb.ru>

On Wed, Apr 24, 2019 at 4:22 PM Kirill Smelkov <kirr@nexedi.com> wrote:
> - FUSE_PRECISE_INVAL_DATA:
>
>     --- b/include/uapi/linux/fuse.h
>     +++ b/include/uapi/linux/fuse.h
>     @@ -266,7 +266,7 @@
>       * FUSE_MAX_PAGES: init_out.max_pages contains the max number of req pages
>       * FUSE_CACHE_SYMLINKS: cache READLINK responses
>       * FUSE_NO_OPENDIR_SUPPORT: kernel supports zero-message opendir
>     - * FUSE_PRECISE_INVAL_DATA: filesystem is fully responsible for data cache invalidation
>     + * FUSE_PRECISE_INVAL_DATA: filesystem is fully responsible for invalidation
>       */
>      #define FUSE_ASYNC_READ                (1 << 0)
>      #define FUSE_POSIX_LOCKS       (1 << 1)
>
> the "data cache" in "for data cache invalidation" has particular meaning
> and semantic: the filesystem promises to explicitly invalidate data of

Right; better name: FUSE_EXPLICIT_INVAL_DATA.  Will push fixed version.

> Your amendment for FOPEN_STREAM in uapi/linux/fuse.h (see above) also
> suggests that it is better to be more explicit in that file.
>
>     --- b/fs/fuse/inode.c
>     +++ b/fs/fuse/inode.c
>     @@ -913,13 +913,8 @@
>                                     fc->dont_mask = 1;
>                             if (arg->flags & FUSE_AUTO_INVAL_DATA)
>                                     fc->auto_inval_data = 1;
>     -                       if (arg->flags & FUSE_PRECISE_INVAL_DATA)
>     +                       else if (arg->flags & FUSE_PRECISE_INVAL_DATA)
>                                     fc->precise_inval_data = 1;
>     -                       if (fc->auto_inval_data && fc->precise_inval_data) {
>     -                               pr_warn("filesystem requested both auto and "
>     -                                       "precise cache control - using auto\n");
>     -                               fc->precise_inval_data = 0;
>     -                       }
>                             if (arg->flags & FUSE_DO_READDIRPLUS) {
>                                     fc->do_readdirplus = 1;
>                                     if (arg->flags & FUSE_READDIRPLUS_AUTO)
>
> Even though it is ok for me personally (I could be careful and use only
> FUSE_PRECISE_INVAL_DATA) I still think usage of both "auto" and "precise"
> invalidation modes deserves a warning. It is only at filesystem init time. What
> is the reason not to print it?

The warning makes no sense.  It should either be failure or silent override.

> - "fuse: retrieve: cap requested size to negotiated max_write"
>
>      Signed-off-by: Kirill Smelkov <kirr@nexedi.com>
>      Cc: Han-Wen Nienhuys <hanwen@google.com>
>      Cc: Jakob Unterwurzacher <jakobunt@gmail.com>
>     -Cc: <stable@vger.kernel.org> # v2.6.36+
>
> what is the reason not to include this patch into stable series?

This doens't fix any bugs out there, but there is a slight chance of
regression (so it might possibly have to be reverted in the future) so
it absolutely makes no sense to backport it to stable.

Thanks,
Miklos