On May 28, 2008 10:04 -0700, Joel Becker wrote:
> It's not about net reduction of code. It's about a readable and
> understandable interface. "Pass this array of extent structures we'll
> ignore if you set this special flag" is pretty ugly. Calling FIECOUNT
> separately is nice. How it is implemented in the kernel is a whole
> 'nother ball of wax - maybe we don't have ->fiecount() and always
> implement FIECOUNT in terms of a ->fiemap() walk. Doesn't matter.
In the FIEMAP + NUM_EXTENTS count, you don't need to pass the array of
structures, just the header. I don't think this is an onerous interface:
struct fiemap fiemap = { .fm_start = 0, .fm_length = ~0ULL,
.fm_num_extents = 0,
.fm_flags = FIEMAP_FLAG_NUM_EXTENTS }
rc = ioctl(fd, FIEMAP, &fiemap);
if (rc == 0)
num_extents = fiemap.fm_mapped_extents;
We wouldn't need to even specify .fm_num_extents, if the VFS handler
doesn't check its validity for FIEMAP_FLAG_NUM_EXTENTS (contrary to
my recent change proposal).
Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.
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