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From: Trond Myklebust <trond.myklebust@fys.uio.no>
To: Linus Torvalds <torvalds@osdl.org>
Cc: Ulrich Drepper <drepper@redhat.com>,
	Linux Kernel <linux-kernel@vger.kernel.org>
Subject: Re: statfs() / statvfs() syscall ballsup...
Date: Thu, 9 Oct 2003 19:31:02 -0400	[thread overview]
Message-ID: <16261.61366.97329.707780@charged.uio.no> (raw)
In-Reply-To: <Pine.LNX.4.44.0310091525200.20936-100000@home.osdl.org>

>>>>> " " == Linus Torvalds <torvalds@osdl.org> writes:

    >> Note that f_bsize is usually larger than f_frsize, hence
    >> conversions from the former to the latter are subject to
    >> rounding errors...

     > User space shouldn't know or care about frsize, and it doesn't
     > even necessarily make any sense on a lot of filesystems, so
     > make it easy for the user. It's not as if the rounding errors
     > really matter.

It can lead to funny quirks when doing df: Used + Available != Total

Granted the effects won't be enormous (typically you'll see between 1
and 63 blocks off in the case of NFS w/ 32kwsize and 512byte frsize)
but people get upset about this. That was the reason for adding an
f_frsize field in the first place...

Note: one solution might be to swap the positions of f_frsize and
f_bsize in the kernel struct that is passed up to userland. I.e. pass
up

 struct statfs {
         __u32 f_type;
-         __u32 f_bsize;
+         __u32 f_frsize;
         __u32 f_blocks;
         __u32 f_bfree;
         __u32 f_bavail;
         __u32 f_files;
         __u32 f_ffree;
         __kernel_fsid_t f_fsid;
         __u32 f_namelen;
-         __u32 f_frsize;
+         __u32 f_bsize;
         __u32 f_spare[5];
 };

That will give correct values for the f_bfree, f_bavail,... in the
legacy statfs() case for all existing filesystems.

glibc's statvfs() can then do the correct thing if it detects a >=2.6.0
kernel. It needs to do a copy to its private statvfs struct anyway.

Cheers,
  Trond

  parent reply	other threads:[~2003-10-09 23:31 UTC|newest]

Thread overview: 64+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2003-10-09 22:16 Trond Myklebust
2003-10-09 22:26 ` Linus Torvalds
2003-10-09 23:19   ` Ulrich Drepper
2003-10-10  0:22     ` viro
2003-10-10  4:49       ` Jamie Lokier
2003-10-10  5:26         ` Trond Myklebust
2003-10-10 12:37           ` Jamie Lokier
2003-10-10 13:46             ` Trond Myklebust
2003-10-10 14:35               ` Jamie Lokier
2003-10-10 15:32                 ` Misc NFSv4 (was Re: statfs() / statvfs() syscall ballsup...) Trond Myklebust
2003-10-10 15:53                   ` Jamie Lokier
2003-10-10 16:07                     ` Trond Myklebust
2003-10-10 15:55                   ` Michael Shuey
2003-10-10 16:20                     ` Trond Myklebust
2003-10-10 16:45                     ` J. Bruce Fields
2003-10-10 14:39               ` statfs() / statvfs() syscall ballsup Jamie Lokier
2003-10-09 23:31   ` Trond Myklebust [this message]
2003-10-10 12:27   ` Joel Becker
2003-10-10 14:59     ` Linus Torvalds
2003-10-10 15:27       ` Joel Becker
2003-10-10 16:00         ` Linus Torvalds
2003-10-10 16:26           ` Joel Becker
2003-10-10 16:50             ` Linus Torvalds
2003-10-10 17:33               ` Joel Becker
2003-10-10 17:51                 ` Linus Torvalds
2003-10-10 18:13                   ` Joel Becker
2003-10-10 16:27           ` Valdis.Kletnieks
2003-10-10 16:33           ` Chris Friesen
2003-10-10 17:04             ` Linus Torvalds
2003-10-10 17:07               ` Linus Torvalds
2003-10-10 17:21                 ` Joel Becker
2003-10-10 16:01         ` Jamie Lokier
2003-10-10 16:33           ` Joel Becker
2003-10-10 16:58             ` Chris Friesen
2003-10-10 17:05               ` Trond Myklebust
2003-10-10 17:20               ` Joel Becker
2003-10-10 17:33                 ` Chris Friesen
2003-10-10 17:40                 ` Linus Torvalds
2003-10-10 17:54                   ` Trond Myklebust
2003-10-10 18:05                     ` Linus Torvalds
2003-10-10 20:40                       ` Trond Myklebust
2003-10-10 21:09                         ` Linus Torvalds
2003-10-10 22:17                           ` Trond Myklebust
2003-10-11  2:53                     ` Andrew Morton
2003-10-11  3:47                       ` Trond Myklebust
2003-10-10 18:05                   ` Joel Becker
2003-10-10 18:31                     ` Andrea Arcangeli
2003-10-10 20:33                     ` Helge Hafting
2003-10-10 20:07             ` Jamie Lokier
2003-10-12 15:31             ` Greg Stark
2003-10-12 16:13               ` Linus Torvalds
2003-10-12 22:09                 ` Greg Stark
2003-10-13  8:45                   ` Helge Hafting
2003-10-15 13:25                     ` Ingo Oeser
2003-10-15 15:03                       ` Greg Stark
2003-10-15 18:37                         ` Helge Hafting
2003-10-16 10:29                         ` Ingo Oeser
2003-10-16 14:02                           ` Greg Stark
2003-10-21 11:47                             ` Ingo Oeser
2003-10-10 18:20           ` Andrea Arcangeli
2003-10-10 18:36             ` Linus Torvalds
2003-10-10 19:03               ` Andrea Arcangeli
2003-10-09 23:16 ` Andreas Dilger
2003-10-09 23:24   ` Linus Torvalds

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