[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
bug#29038: df hangs on fifos/named pipes
From: |
Stephane Chazelas |
Subject: |
bug#29038: df hangs on fifos/named pipes |
Date: |
Sat, 28 Oct 2017 08:18:11 +0100 |
User-agent: |
Mutt/1.5.24 (2015-08-30) |
test case:
mkfifo p
df p
That hangs, unless you make "p" non-readable or some other process
has the fifo open in write mode.
The reason is that df tries to open the fifo in read-only mode,
according to comments in the source code so as to trigger a
potential automout.
That goes back to this commit:
> commit dbd17157d7e693b8de9737f802db0e235ff5a3e6
> Author: Tomas Smetana <address@hidden>
> Date: Tue Apr 28 11:21:49 2009 +0200
>
> df: use open(2), not stat, to trigger automounting
>
> * src/df.c (main): When iterating over command-line arguments,
> attempting to ensure each backing file system is mounted, use
> open, not stat. stat is no longer sufficient to trigger
> automounting, in some cases. Based on a suggestion from Ian Kent.
> More details in http://bugzilla.redhat.com/497830
More info at the bugzilla link.
It's arguable whether df, a reporting tool, should have such a
side effect as automounting a file system.
The fifo issue though is a bug IMO, especially considering that
POSIX explicitely says that df should work on fifos.
Here, it may be enough to add the O_DIRECTORY flag to open()
where available if we only care about automounting files of type
directory (or portably use opendir()).
Or use O_PATH on Linux 3.6+ followed by openat() on non-fifos if
open(O_PATH) is not enough to trigger the automount in the
unlikely event we care about automounting non-directory files
(and report their disk usage).
Or not open() at all, and not automount file systems.
Note that busybox, heirloom or ast-open df implementations on
Linux don't have the problem (and presumably don't automount
file systems). Nor does FreeBSD.
Reproduced with:
$ df --version
df (GNU coreutils) 8.25
and:
$ df --version
df (GNU coreutils) 8.27.46-e13fe
That was discovered by Martijn Dekker, CCed, when looking for a
portable way to identify the file system of an arbitrary file.
--
Stephane
- bug#29038: df hangs on fifos/named pipes,
Stephane Chazelas <=