linux-kernel - Re: [RESEND4, PATCH 1/2] fuse: retrieve: cap requested size to negotiated max

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Date:   Wed, 24 Apr 2019 17:02:42 +0200
From:   Miklos Szeredi <miklos@...redi.hu>
To:     Kirill Smelkov <kirr@...edi.com>
Cc:     Miklos Szeredi <mszeredi@...hat.com>,
        Han-Wen Nienhuys <hanwen@...gle.com>,
        Jakob Unterwurzacher <jakobunt@...il.com>,
        Kirill Tkhai <ktkhai@...tuozzo.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        fuse-devel <fuse-devel@...ts.sourceforge.net>,
        stable <stable@...r.kernel.org>
Subject: Re: [RESEND4, PATCH 1/2] fuse: retrieve: cap requested size to
 negotiated max_write

On Wed, Apr 24, 2019 at 4:22 PM Kirill Smelkov <kirr@...edi.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@...edi.com>
>      Cc: Han-Wen Nienhuys <hanwen@...gle.com>
>      Cc: Jakob Unterwurzacher <jakobunt@...il.com>
>     -Cc: <stable@...r.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