Hi Andrew and Alexander,
I have implemented the ioctls for the filesystem freeze feature
and discussed its implementation on the ML (linux-ext4, xfs,
linux-fsdevel, linux-kernel) for five months. All of the comments are
addressed in my patch-set.
Could you consider merging it into Linux?
The filesystem freeze feature can suspend accesses to the filesystem
keeping the filesystem's consistency. We can take the consistent backup
with it cooperating with the backup software.
The patches are re-based from linux-2.6.26-rc3 to linux-2.6.26-rc7
There is no functional change from the previous version.
The patch-set consists of the following three patches.
[PATCH 1/3] Implement generic freeze feature
I have modified to set the suitable error number (EOPNOTSUPP)
in case the filesystem doesn't support the freeze feature.
The ioctls for the generic freeze feature are below.
o Freeze the filesystem
int ioctl(int fd, int FIFREEZE, arg)
fd: The file descriptor of the mountpoint
FIFREEZE: request code for the freeze
arg: Ignored
Return value: 0 if the operation succeeds. Otherwise, -1
o Unfreeze the filesystem
int ioctl(int fd, int FITHAW, arg)
fd: The file descriptor of the mountpoint
FITHAW: request code for unfreeze
arg: Ignored
Return value: 0 if the operation succeeds. Otherwise, -1
[PATCH 2/3] Remove XFS specific ioctl interfaces for freeze feature
It removes XFS specific ioctl interfaces and request codes
for freeze feature.
This patch has been supplied by David Chinner.
[PATCH 3/3] Add timeout feature
The timeout feature is added to freeze ioctl. And new ioctl
to reset the timeout period is added.
o Freeze the filesystem
int ioctl(int fd, int FIFREEZE, long *timeval)
fd: The file descriptor of the mountpoint
FIFREEZE: request code for the freeze
timeval: the timeout period in seconds
If it's 0 or 1, the timeout isn't set.
This special case of "1" is implemented to keep
the compatibility with XFS applications.
Return value: 0 if the operation succeeds. Otherwise, -1
o Reset the timeout period
This is useful for the application to set the timeval more accurately.
For example, the freezer resets the timeval to 10 seconds every 5
seconds. In this approach, even if the freezer causes a deadlock
by accessing the frozen filesystem, it will be solved by the timeout
in 10 seconds and the freezer can recognize that at the next reset
of timeval.
int ioctl(int fd, int FIFREEZE_RESET_TIMEOUT, long *timeval)
fd:file descriptor of mountpoint
FIFREEZE_RESET_TIMEOUT: request code for reset of timeout period
timeval: new timeout period in seconds
Return value: 0 if the operation succeeds. Otherwise, -1
Error number: If the filesystem has already been unfrozen,
errno is set to EINVAL.
Any comments are very welcome.
Cheers, Takashi
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