From: Andy Lutomirski <luto@mit.edu>
To: Nick Piggin <npiggin@suse.de>
Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
Al Viro <viro@ZenIV.linux.org.uk>,
Ulrich Drepper <drepper@redhat.com>,
Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [rfc] new stat*fs-like syscall?
Date: Thu, 24 Jun 2010 10:08:55 -0400 [thread overview]
Message-ID: <4C2366F7.5010200@mit.edu> (raw)
In-Reply-To: <20100624131455.GA10441@laptop>
Nick Piggin wrote:
> This has come up a few times in the past, and I'd like to try to get
> an agreement on it. statvfs(2) importantly contains f_flag (mount
> flags), and is encouraged to use rather than statfs(2). The kernel
> provides a statfs syscall only.
>
> This means glibc has to provide f_flag support by parsing /proc/mounts
> and stat(2)ing mount points. This is really slow, and /proc/mounts is
> hard for the kernel to provide. It's actually the last scalability
> bottleneck in the core vfs for dbench (samba) after my patches.
>
> Not only that, but it's racy.
>
> Other than types, other differences are:
> - statvfs(2) has is f_frsize, which seems fairly useless.
> - statvfs(2) has f_favail.
> - statfs(2) f_bsize is optimal transfer block, statvfs(2) f_bsize is fs
> block size. The latter could be useful for disk space algorithms.
> Both can be ill defned.
> - statvfs(2) lacks f_type.
>
> Is there anything more we should add here? Samba wants a capabilities
> field, with things like sparse files, quotas, compression, encryption,
> case preserving/sensitive.
>
> Any thoughts?
Something like fsid but actually specified to uniquely identify a
superblock. (Currently, fsid seems to be set by the filesystem, and
nothing in particular ensures that two different filesystems couldn't
have collisions.) We could guarantee (or have a flag guaranteeing) that
(fsid, st_inode) actually uniquely identifies an inode.
Similarly, something like fsid that uniquely identifies the vfsmount
could be useful, although I don't know how easy that would be to provide
for fstat?fs.
If we could expose the complete set of filesystem mount options so that
mount(1) didn't have to look at /proc/self/mounts or /etc/mtab, then
playing with chroots would be that much easier.
Should we expose superblock and vfsmount options separately? We have
read-only bind mounts now, but the way they work is rather inscrutable,
and if stat?fs could say "superblock is read-write but vfsmount is
readonly" then people might be able to make more sense of what's going on.
--Andy
next prev parent reply other threads:[~2010-06-24 14:15 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-06-24 13:14 [rfc] new stat*fs-like syscall? Nick Piggin
2010-06-24 14:03 ` Miklos Szeredi
2010-06-24 14:36 ` Nick Piggin
2010-06-24 14:08 ` Andy Lutomirski [this message]
2010-06-24 14:18 ` Miklos Szeredi
2010-06-24 14:37 ` Andrew Lutomirski
2010-06-24 14:48 ` Miklos Szeredi
2010-06-25 3:50 ` Nick Piggin
2010-06-24 23:06 ` Andreas Dilger
2010-06-25 6:37 ` Christoph Hellwig
2010-06-24 23:13 ` Andreas Dilger
2010-06-25 4:01 ` Nick Piggin
2010-06-25 4:33 ` Jeff Garzik
2010-06-25 17:47 ` Andreas Dilger
2010-06-25 17:52 ` Ulrich Drepper
2010-06-25 18:16 ` Christoph Hellwig
2010-06-25 18:45 ` Christoph Hellwig
2010-06-25 19:40 ` Ulrich Drepper
2010-06-26 5:53 ` J. R. Okajima
2010-06-26 9:35 ` Christoph Hellwig
2010-06-26 12:54 ` J. R. Okajima
2010-07-05 20:58 ` Brad Boyer
2010-07-05 23:31 ` J. R. Okajima
2010-07-06 0:45 ` Brad Boyer
2010-07-06 16:45 ` Linus Torvalds
2010-07-07 1:44 ` Christoph Hellwig
2010-07-07 2:28 ` Linus Torvalds
2010-06-26 14:49 ` Ulrich Drepper
2010-06-26 10:13 ` Andi Kleen
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