[PATCH] fsfreeze: suspend and resume access to an filesystem

[Eric Sandeen]

Masatake YAMATO wrote:
> Hi,
> 
> (The disscussion can be found at
>  http://thread.gmane.org/gmane.linux.utilities.util-linux-ng/3181/focus=3193)
> 
>> Hello.
>>
>> I understand reason when it use with device-mapper.
>> I think, fsfreeze command need for filesystem on physical block device without device-mapper.
>> For example, by storage controller based LUN snapshot.
>>
>> # fsfreeze -f /data
>> # ssh root at 192.168.0.1 "take snapshot lun0"
>> # fsfreeze -u /data
>>
>> * /data is mounted physical block device(/dev/sdb1)
> 
> As Hajime wrote, taking snapshot in physical storage level is popular
> situation. It seems that xfs_freeze can be used for the purpose but
> the name `xfs_freeze' gives the impression that the command is only 
> for xfs. 
> 
> My argument can be applicable to gfs2_tool, too.  "gfs2_tool freeze"
> also does ``ioctl(fd, FIFREEZE, 0)''.
> 
> 
> One of the solution is to add xxx_freeze for each file system implementation
> which has freeze/unfreeze methods to eash util-xxx, xxx-progs or xxx-utils. 
> e.g. Adding ext4_freeze or ext3_freeze command to e2fsprogs package.
> 
> However, I think this is not good idea. Linux provides file system neutral
> interface already. So it is better to have file system neutral command(fsfreeze)
> and the command is included in file system neutral package, util-linux-ng.

I tend to agree, since there is a common interface, there is no reason to
have filesystem-specific tools which all do the same thing.

Note that xfs_freeze existed long before the common interface, and in fact
the common ioctl number was chosen based on the xfs number, so that explains
the existence of the xfs-specific tool, and why it does happen to work
now on non-xfs filesystems....

-Eric