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

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

[Masatake YAMATO]

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@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.

Masatake YAMATO

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Re: [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@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

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