One question to ask is whether a goal inode allocation API would be enough
or if you need specific block allocation, or both? If you could start
allocation at a specific inode, would that be enough to avoid the messy
code below?
Cheers, Andreas
> On Aug 13, 2014, at 15:45, Dmitry Monakhov <dmonakhov@xxxxxxxxxx> wrote:
>
>
> Currently we have not public API for block allocation from some
> specific region (group/flex_group/blk_range). The only existing
> hack is available in migrate.c where we use goal_inode for
> ext4_new_inode().
>
> In fact this tend make some specific task very complicated.
> For example my e4defrag2 utility try to compact small files from
> one group together. In order to allocate blocks from given group
> I have to perform number of crazy stuff, such as:
> 1) Prepare cache of directories according to it's group (where dir_inode
> is placed)
>
> 2) Try to allocate local donor file with local blocks (from given group)
> Pseudo code of donor creation procedure :
> int find_donor(int grp, ...) {
> for (i = 0; i = dir_cache[grp].num;i++) {
> fd = openat(dir_cache[grp].fd[i], "donor", O_CREAT|flags,... )
> fstat(fd, &stat);
> if (inode_group(stat->st_ino) != grp)
> goto next_candidate;
> do_falloc(fd, size);
> /* Check that blocks we allocated are belongs to group we want*/
> if (!is_block_local(fd, group))
> goto next_candidate;
> goto found_donor;
> .....
> }
> .....
> }
> All this machinery is very ugly, unstable and increase code-base about
> 500-700 lines of code. And I want to ask you why we do not have such
> API? AFAIR this API was requested several times, but it was rejected.
> I do understand that this is not good idea to allow unprivileged user to
> manipulate block allocator, but IMHO we can hide it under CAP_RESOURCES
> or CAP_ADMIN.
> Please tell be your opinion. I'll happy to implement that ioctl.
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