On Mon, Oct 21, 2019 at 01:05:06PM -0500, Eric Sandeen wrote:
> On 9/25/19 4:36 PM, Darrick J. Wong wrote:
> > From: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> >
> > In xfs_iterate_filemaps, we query the number of bmaps for a given file
> > that we're going to iterate, so feed that information to bmap so that
> > the kernel won't waste time allocating in-kernel memory unnecessarily.
> >
> > Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> > ---
> > scrub/filemap.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> >
> > diff --git a/scrub/filemap.c b/scrub/filemap.c
> > index bdc6d8f9..aaaa0521 100644
> > --- a/scrub/filemap.c
> > +++ b/scrub/filemap.c
> > @@ -71,7 +71,6 @@ xfs_iterate_filemaps(
> > map->bmv_length = ULLONG_MAX;
> > else
> > map->bmv_length = BTOBB(key->bm_length);
> > - map->bmv_count = BMAP_NR;
> > map->bmv_iflags = BMV_IF_NO_DMAPI_READ | BMV_IF_PREALLOC |
> > BMV_IF_NO_HOLES;
> > switch (whichfork) {
> > @@ -96,6 +95,7 @@ xfs_iterate_filemaps(
> > moveon = false;
> > goto out;
> > }
> > + map->bmv_count = min(fsx.fsx_nextents + 2, BMAP_NR);
>
> Was going to ask you to document the magical +2 here but IRC discussion suggests
> that it is in case fsx_nextents is 0, and we need to send in a count of at least
> 2 (header + 1 structure?)
>
> But if there are no extents, what are we trying to map in the loop below,
> anyway?
Nothing. Will rework it with:
if (fsx_nextents == 0)
return 0;
bmv_count = min(fsx_nextents + 1, BMAP_NR);
while ((error = ioctl(...))) {
--D
> >
> > while ((error = ioctl(fd, XFS_IOC_GETBMAPX, map)) == 0) {
> > for (i = 0, p = &map[i + 1]; i < map->bmv_entries; i++, p++) {
> >
