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From: Miklos Szeredi <miklos@szeredi.hu>
To: Kirill Smelkov <kirr@nexedi.com>
Cc: Miklos Szeredi <mszeredi@redhat.com>,
	linux-fsdevel@vger.kernel.org,
	fuse-devel <fuse-devel@lists.sourceforge.net>,
	Han-Wen Nienhuys <hanwen@google.com>,
	Jakob Unterwurzacher <jakobunt@gmail.com>,
	stable <stable@vger.kernel.org>
Subject: Re: [RESEND, PATCH v2] fuse: Don't drop NOTIFY_REPLY if we promised it
Date: Wed, 27 Feb 2019 21:26:32 +0100	[thread overview]
Message-ID: <CAJfpegus62jktnXhUPSfMfZmxCEArudgkJFSq6iAJYhOAqBAAA@mail.gmail.com> (raw)
In-Reply-To: <20190227200155.GA14682@deco.navytux.spb.ru>

On Wed, Feb 27, 2019 at 9:02 PM Kirill Smelkov <kirr@nexedi.com> wrote:
>
> Miklos, first of all thanks for feedback.
>
> On Tue, Feb 26, 2019 at 04:14:22PM +0100, Miklos Szeredi wrote:
> > On Tue, Feb 19, 2019 at 10:42 AM Kirill Smelkov <kirr@nexedi.com> wrote:
> > >
> > > A successful call to NOTIFY_RETRIEVE by filesystem carries promise from
> > > the kernel to send back NOTIFY_REPLY message. However if the filesystem
> > > is not reading requests with fuse_conn->max_pages capacity,
> >
> > That's a violation of the contract by the fuse server, not the kernel.
>
> Do you mean that even if filesystem server configures via
> init_out.max_write that it is accepting e.g. only 32K max writes, it
> still has to be issuing sys_read with buffer of 128K (= hardcoded
> fuse_conn->max_pages before Linux 4.20, and default since Linux 4.20)?

Filesystem is asking for a specific number of bytes to retrieve.  It
does not have to be less than max_writes, but it does have to fit into
the request buffer it is using.  If the filesystem is asking to
retrieve 64k and it is using a 32k request buffer, then that obviously
won't work.   Kernel could limit the retrieve length to max_writes,
that may make sense, but it doesn't fundamentally change the fact that
if the filesystem is not properly sizing the request buffer, it may
result in various forms of breakage.

Thanks,
Miklos

  reply	other threads:[~2019-02-27 20:26 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-19  9:42 [RESEND, PATCH v2] fuse: Don't drop NOTIFY_REPLY if we promised it Kirill Smelkov
2019-02-26 15:14 ` Miklos Szeredi
2019-02-27 20:02   ` Kirill Smelkov
2019-02-27 20:26     ` Miklos Szeredi [this message]
2019-02-27 20:39       ` Kirill Smelkov
2019-02-28  8:10         ` Miklos Szeredi
2019-02-28 11:48           ` Kirill Smelkov
2019-02-28 11:50             ` [PATCH 2/2] fuse: require /dev/fuse reads to have enough buffer capacity as negotiated Kirill Smelkov
2019-03-07  9:34             ` [RESEND, PATCH v2] fuse: Don't drop NOTIFY_REPLY if we promised it Kirill Smelkov
2019-03-14 10:45               ` [RESEND3, PATCH 0/2] fuse: don't stuck clients on retrieve_notify with size > max_write Kirill Smelkov
2019-03-14 10:46                 ` [PATCH 1/2] fuse: retrieve: cap requested size to negotiated max_write Kirill Smelkov
2019-03-14 10:46                 ` [PATCH 2/2] fuse: require /dev/fuse reads to have enough buffer capacity as negotiated Kirill Smelkov

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