linux-kernel - Re: [PATCH 2/9] vfs: export do_splice

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Message-ID: <29635.1363782649@warthog.procyon.org.uk>
Date:	Wed, 20 Mar 2013 12:30:49 +0000
From:	David Howells <dhowells@...hat.com>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	dhowells@...hat.com, Jan Kara <jack@...e.cz>,
	Miklos Szeredi <miklos@...redi.hu>,
	torvalds@...ux-foundation.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, hch@...radead.org,
	akpm@...ux-foundation.org, apw@...onical.com, nbd@...nwrt.org,
	neilb@...e.de, jordipujolp@...il.com, ezk@....cs.sunysb.edu,
	sedat.dilek@...glemail.com, hooanon05@...oo.co.jp, mszeredi@...e.cz
Subject: Re: [PATCH 2/9] vfs: export do_splice_direct() to modules

Al Viro <viro@...IV.linux.org.uk> wrote:

> fs/cachefiles/rdwr.c:967:                       ret = file->f_op->write(
> 
> cachefiles_write_page(); no fucking idea what locks might be held by caller
> and potentially that's a rather nasty source of PITA

The caller of cachefiles_write_page() (ie. fscache_write_op()) holds no locks
over the call.

__fscache_write_page() queues the pages for writing to the cache from the
netfs's read-side routines and returns immediately.

fscache_write_op() then picks them up in the background and passes them over
to the backend (eg. cachefiles_write_page()) which writes them out to the
cache.

So I think it should be safe to call file_start/end_write() or whatever around
the file->f_op->write() calls.

David
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