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stat.2: Add note about stat() being racy 

The same thing was fixed for execve() in kernel commit
8b01fc86b9f425899f8a3a8fc1c47d73c2c20543, but for performance
reasons, that simple patch won't work for stat().

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Jann Horn 2015-04-20 22:46:01 +02:00 committed by Michael Kerrisk
parent 9e1d8950a2
commit f240296dee
1 changed files with 23 additions and 0 deletions
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man2/stat.2
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@ -175,6 +175,29 @@ that may be present between some fields on various architectures.
Consult the glibc and kernel source code
if you need to know the details.
\# Background: inode attributes are modified with i_mutex held, but
\# read by stat() without taking the mutex.
.I Note:
For performance and simplicity reasons, different fields in the
.I stat
structure may contain state information from different moments
during the execution of the syscall. For example, if
.IR st_mode ,
.IR st_uid
and
.IR st_gid
are changed by another process by calling
.BR chown (2) ,
.BR stat ()
might return the old
.I st_mode
together with the new
.IR st_uid ,
or the old
.I st_uid
together with the new
.IR st_mode .
The
.I st_dev
field describes the device on which this file resides.