doc update and stop setting MAGIC_PRESERVE_ATIME #2335
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Signed-off-by: Quentin Armitage <[email protected]>
On RedHat systems setting MAGIC_PRESERVE_ATIME caused SELinux errors. RedHat bugzilla identified in BZ https://bugzilla.redhat.com/show_bug.cgi?id=1997148 that this was caused by a call to utimensat(). Issue acassen#2333 identified that setting MAGIC_PRESERVE_ATIME triggers the call of utimensat(). Inspecting src/magic.c in the "file" utility source code shows that the call of utimensat() was made due to utimes() being called. glibc maps this to a call of utimensat(). Although setting the flag, and hence preserving atime when ascertaining the file type is not unreasonable, the atime will be modified anyway when the file is subsequently executed. Also it is clear from the "file" code in src/magic.c, that not only is the atime not properly restored when MAGIC_PRESERVE_ATIME is set, but that mtime is also modified, even though the file has not been modified. This is due to close_and_restore() in src/magic.c only restoring the seconds field, and not the microseconds that utimes() can specify, and that utime()/utimes() update both the atime and mtime fields. Consequently the fractions of a second of atime and mtime are both set to 0. Further, there is a comment in src/magic.c: /* * Try to restore access, modification times if read it. * This is really *bad* because it will modify the status * time of the file... And of course this will affect * backup programs */ We don't want to be doing *bad* things in keepalived, so that reinforces removing MAGIC_PRESERVE_ATIME. Signed-off-by: Quentin Armitage <[email protected]>
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