On Wed 19-01-11 11:42:50, Lukas Czerner wrote:

On Wed, 19 Jan 2011, Tao Ma wrote:

quoted

From: Tao Ma <redacted>

We adjust 'len' with s_first_data_block - start in case of start is less
than s_first_data_block, but it could underflow in case blocksize=1K, while
fstrim_range.len=512 and fstrim_range.start = 0. In this case len happens
to be underflow and in the end, although we are safe that last_group check
will limit the trim to the whole volume, I am afraid that isn't what the user
really want.

So this patch fix it. It also adds a new variable s_first_data_block so that
the 4 le32_to_cpu can be replaced with 1.

Well, I just realized that what are we doing is not exactly what will
user expect. User does not really care where the first data block is.
What the user will expect is, to trim let's say first one gigabyte
of his filesystem, not gigabyte - first data block.

So what I suggest is to always add first_data_block to
fstrim_range.start and do all the necessary checks for overflow. If no
one has any objections I'll put it to the patch.

  Well, since we speak about at most 1KB (s_first_data_block is non-zero
only when blocksize == 1024 and in that case it is 1), I don't think it
really matters and I don't mind whatever solution. What user expects is
a bit hard to guess (whether he views 'start' as a start of the filesystem
or a start of the device). Maybe the former makes a tad bit more sense
but as I said I don't really care so since you're the author of the code I
leave it up to you.

								Honza
-- 
Jan Kara [off-list ref]
SUSE Labs, CR