Hello Christoph,
Thanks for your review comments.
On 4/24/20 3:41 PM, Christoph Hellwig wrote:
I think the right fix is to move fiemap_check_ranges into all the ->fiemap
I do welcome your suggestion here. But I am not sure of what you are
suggesting should be done as a 1st round of changes for the immediate
reported problem.
So currently these patches take the same approach on overlayfs on how
VFS does it. So as a fix to the overlayfs over ext4 reported problems in
thread [1] & [2]. I think these patches are doing the right thing.
Also maybe I am biased in some way because as I see these are the right
fixes with minimal changes only at places which does have a direct
problem.
But I do agree that in the second round (as a right approach for the
long term), we could just get rid of fiemap_check_ranges() from
ioctl_fiemap() & ovl_fiemap(), and better add those in all filesystem
specific implementations of ->fiemap() call.
(e.g. ext4_fiemap(), f2fs_fiemap() etc.).
instances (we only have a few actual implementation minus the wrappers
around iomap/generic).
>
Ok, got it. So for filesystem specific ->fiemap implementations,
we should add fiemap_check_ranges() in there implementations.
And for those FS which are calling iomap_fiemap() or
generic_block_fiemap(), what you are suggesting it to add
fiemap_check_ranges() in iomap_fiemap() & generic_block_fiemap().
Is this understanding correct?
Then add a version if iomap_fiemap that can pass
in maxbytes explicitly for ext4, similar to what we've done with various
other generic helpers.
Sorry I am not sure if I followed it correctly. Help me understand pls.
Also some e.g about "what we've done with various other generic helpers"
iomap_fiemap(), will already get a FS specific inode from which we can
calculate inode->i_sb->s_maxbytes. So why pass maxbytes explicitly?
The idea of validating input against file systems specific paramaters
before we call into the fs is just bound to cause problems.
Sure, but as I was saying. The changes you are suggesting will have
changes in all filesystem's individual ->fiemap() implementations.
But as a fix for the reported problem of [1] & [2], I think these
patches could be taken. Once those are merged, I can work on the changes
that you are suggesting.
Does that sound ok to you?
[1]: https://lkml.org/lkml/2020/4/11/46
[2]:
https://patchwork.ozlabs.org/project/linux-ext4/patch/20200418233231.z767yvfiupy7hwgp@xxxxxxxxxxxxxxxxxxxxxxxxx/
-ritesh
