From: Andrew Gallagher <agallagher@fb.com>
Date: Tue, 5 Nov 2013 15:05:52 +0000 (+0100)
Subject: fuse: support clients that don't implement 'open'
X-Git-Tag: v3.14-rc1~121^2
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=7678ac50615d;p=pandora-kernel.git

fuse: support clients that don't implement 'open'

open/release operations require userspace transitions to keep track
of the open count and to perform any FS-specific setup.  However,
for some purely read-only FSs which don't need to perform any setup
at open/release time, we can avoid the performance overhead of
calling into userspace for open/release calls.

This patch adds the necessary support to the fuse kernel modules to prevent
open/release operations from hitting in userspace. When the client returns
ENOSYS, we avoid sending the subsequent release to userspace, and also
remember this so that future opens also don't trigger a userspace
operation.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
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