On 01/19/2011 06:42 PM, 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.

It is hard to tell, anyway, it is just 1kb(in case bs=1k and 
first_data_block != 0), so I guess either is ok. ;)

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.

I am fine with it. And it should make the code more clear and easy to 
read I guess.

Regards,
Tao