>>>>> Ryusuke Konishi writes:
>>>>> On Thu, 14 Jun 2012 11:22:17 +0700, Ivan Shmakov wrote:
>>>>> Ryusuke Konishi writes:
[…]
>>> Implementing Off-line resizing is a bit tough task because it
>>> requires a user space library to read internal meta data of the
>>> nilfs file system and append updated blocks to it.
… I guess that a user-level toolkit akin to e2fsprogs would be
handy anyway. (Shouldn't there be an fsck(8) for NILFS, BTW?)
Other than resizing, there could be a feature to “split” a
filesystem — take one or more “snapshot” checkpoints and make a
copy of the parts of the filesystem “reachable” from these
checkpoints on a distinct block device (perhaps of a differing
size), which seems like one more way to do backups.
>>> This is almost equivalent to implementing kernel functions of nilfs
>>> in user land.
[…]
>> I wonder, how complicated this task would be? In particular, do I
>> need to alter all the segments to resize filesystem, or only
>> specific ones? Also, are these internal metadata records just “a
>> bunch of C structs”, or something more complex?
> This needs at least the following tasks:
> 1) Update two super blocks to increase/decrease the number of total
> segments and the device size. (easy)
> 2) Update segment usage information to adjust free segment count of
> nilfs_sufile_header struct (sh_ncleansegs) which is written in
> the segment usage file. (Sadly not easy)
> 3) If truncating in-use segments, relocating blocks and updating disk
> address translation information are also needed. (very hard)
ACK. (Fortunately, I'm not that interested in shrinking
filesystems right now.)
> For reference, a discussion on this topic is found in the archives of
> the list:
> http://marc.info/?t=128419843600003&r=1&w=2
ACK, thanks! I hope to take a closer look at this problem
within two weeks or so.
(JFTR: those reading via Gmane may access the thread via either
of [1, 2]; the first message in the thread is [3].)
[1] http://comments.gmane.org/gmane.comp.file-systems.nilfs.user/397
[2] http://thread.gmane.org/gmane.comp.file-systems.nilfs.user/397/focus=1686
[3] news:baefa5609cc3ab4bae1625cad4c27e5c02986...@tdpost.td.tandbergdata.com
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