Re: [fuse-devel] delta filesystem prototype

[Goswin von Brederlow <goswin-v-b@web.de>]

hooanon05@yahoo.co.jp writes:

> Goswin von Brederlow:
>> I could think of three possible values:
>> 
>> 1) the sum of the st_blocks of both branches (total space used)
>> 2) min(size/blocksize, sum of st_blocks) (appox. what the file would use)
>> 3) st_bocks of read-write branch (read-write space used only)
>
> 4) calculate st_blocks by merging based upon bitmap (dmpath)
>
> Some applications may not like st_blksize either since it may be
> different per block.
>
> One more difficulty (hard to support issue).
> - open a file on deltafs
> - unlink it
> - rmdir its parent
> - write or fchmod to it
> - rewind+read or mmap+read from the opened file
> - cat it be read correctly?
>
>
> J. R. Okajima

For unlink and rmdir you need whiteout files.

For all the rest you just have to keep the file descriptor(s) alive as
long as the file is opened and cache metadat in the internal FD
structure.

It isn't trivial but it isn't really hard.

MfG
        Goswin