* [Bug 18372] New: A filled up named pipe always has a size of zero!
@ 2010-09-12 21:47 bugzilla-daemon
2012-05-12 15:46 ` [Bug 18372] " bugzilla-daemon
2012-05-12 15:46 ` bugzilla-daemon
0 siblings, 2 replies; 3+ messages in thread
From: bugzilla-daemon @ 2010-09-12 21:47 UTC (permalink / raw)
To: linux-ext4
https://bugzilla.kernel.org/show_bug.cgi?id=18372
Summary: A filled up named pipe always has a size of zero!
Product: File System
Version: 2.5
Kernel Version: 2.6.32-22-generic (also older and newer ones)
Platform: All
OS/Version: Linux
Tree: Mainline
Status: NEW
Severity: high
Priority: P1
Component: ext4
AssignedTo: fs_ext4@kernel-bugs.osdl.org
ReportedBy: tom.bzliknl83947@online.de
CC: tom.bzliknl83947@online.de
Regression: No
Hi, there!
The size of a filled named pipe is always zero. This is wrong! A read operation
is going to hang for try to read from an empty pipe. To go around this trap it
is necessary to do a conditional test on the filesize, [ -s pipe ]. Problem:
The test doesn't work, because filesize is always zero.
Try:
mknod pipe &
sleep 3600 <>pipe &
echo 'date' >pipe
[ -s pipe ] && echo "filled up"
ls -l pipe; stat pipe # if size zero, it is wrong
[ -s pipe ] && (read val <pipe; echo $val)
This is a critical error. While parallel processing a script would be blocked.
In worst case it causes a deadlock situation. Every changing of a condition of
a file should be reported whithin the i-node.
I found it in several disto: Ubuntu KarmicKoala 9.1, LucidLynx 10.04,
Linux Mint Debian Edition 5, Slackware 13.1 x64
Best regards
TOM
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