reduce bmv_count in xfs_vn_fiemap

commit 6321e3ed2acf3ee9643cdd403e1c88605d7944ba caused the full bmv_count's worth of getbmapx structures to get allocated; telling it to do MAXEXTNUM was a bit insane, resulting in ENOMEM.

Chop it down to something reasonable, the caller can loop over this if the file has > 64 extents.

(this is a regression, FWIW)

Signed-off-by Eric Sandeen <[email protected]>

---

iff --git a/fs/xfs/linux-2.6/xfs_iops.c b/fs/xfs/linux-2.6/xfs_iops.c index 58973bb..370e9a7 100644

fs/xfs/linux-2.6/xfs_iops.c +6 -2

@@ -680,8 +680,12 @@ xfs_vn_fiemap(
 	else
 		bm.bmv_length = BTOBB(length);
 
-	/* our formatter will tell xfs_getbmap when to stop. */
-	bm.bmv_count = MAXEXTNUM;
+	/*
+	 * xfs_getbmap allocates based on that; pick a count that's
+	 * not too outragous.
+	 * Our formatter will tell xfs_getbmap when to stop.
+	 */
+	bm.bmv_count = 64;
 	bm.bmv_iflags = BMV_IF_PREALLOC;
 	if (fieinfo->fi_flags & FIEMAP_FLAG_XATTR)
 		bm.bmv_iflags |= BMV_IF_ATTRFORK;

Quoted 4 lines · Eric Sandeen

commit 6321e3ed2acf3ee9643cdd403e1c88605d7944ba caused the full bmv_count's worth of getbmapx structures to get allocated; telling it to do MAXEXTNUM was a bit insane, resulting in ENOMEM.

Quoted 2 lines

Chop it down to something reasonable, the caller can loop over this if the file has > 64 extents.

It does seem to me that this will result in an unusal case for the caller, in that it will get fewer extents than fit in the provided buffer, yet should loop. Do current callers know that they can hit this case, detect it, and loop accordingly? Or is this just pushing the problem/regression to userspace?

commit 6321e3ed2acf3ee9643cdd403e1c88605d7944ba caused the full bmv_count's worth of getbmapx structures to get allocated; telling it to do MAXEXTNUM was a bit insane, resulting in ENOMEM every time.

Chop it down to something reasonable, the number of slots in the caller's input buffer. If this is too large the caller may get ENOMEM but the reason should not be a mystery, and they can try again with something smaller.

Signed-off-by Eric Sandeen <[email protected]>

---

V2: set it to the fiemap info's fi_extents_max

fs/xfs/linux-2.6/xfs_iops.c +1 -2

index 58973bb..954d701 100644
@@ -680,8 +680,7 @@ xfs_vn_fiemap(
 	else
 		bm.bmv_length = BTOBB(length);
 
-	/* our formatter will tell xfs_getbmap when to stop. */
-	bm.bmv_count = MAXEXTNUM;
+	bm.bmv_count = fieinfo->fi_extents_max;
 	bm.bmv_iflags = BMV_IF_PREALLOC;
 	if (fieinfo->fi_flags & FIEMAP_FLAG_XATTR)
 		bm.bmv_iflags |= BMV_IF_ATTRFORK;

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commit 6321e3ed2acf3ee9643cdd403e1c88605d7944ba caused the full bmv_count's worth of getbmapx structures to get allocated; telling it to do MAXEXTNUM was a bit insane, resulting in ENOMEM every time.

Chop it down to something reasonable, the number of slots in the caller's input buffer. If this is too large the caller may get ENOMEM but the reason should not be a mystery, and they can try again with something smaller.

We add 1 to the value because in the normal getbmap world, bmv_count includes the header and xfs_getbmap does:

        nex = bmv->bmv_count - 1;
        if (nex <= 0)
                return XFS_ERROR(EINVAL);

Signed-off-by Eric Sandeen <[email protected]>

---

V2: set it to the fiemap info's fi_extents_max
V3: bump up by one to accomodate expected bmv header in core

fs/xfs/linux-2.6/xfs_iops.c +1 -2

index 58973bb..954d701 100644
@@ -680,8 +680,7 @@ xfs_vn_fiemap(
 	else
 		bm.bmv_length = BTOBB(length);
 
-	/* our formatter will tell xfs_getbmap when to stop. */
-	bm.bmv_count = MAXEXTNUM;
+	bm.bmv_count = fieinfo->fi_extents_max + 1;
 	bm.bmv_iflags = BMV_IF_PREALLOC;
 	if (fieinfo->fi_flags & FIEMAP_FLAG_XATTR)
 		bm.bmv_iflags |= BMV_IF_ATTRFORK;

V3: bump up by one to accomodate expected bmv header in core

commit 6321e3ed2acf3ee9643cdd403e1c88605d7944ba caused the full bmv_count's worth of getbmapx structures to get allocated; telling it to do MAXEXTNUM was a bit insane, resulting in ENOMEM every time.

Chop it down to something reasonable, the number of slots in the caller's input buffer. If this is too large the caller may get ENOMEM but the reason should not be a mystery, and they can try again with something smaller.

We add 1 to the value because in the normal getbmap world, bmv_count includes the header and xfs_getbmap does:

        nex = bmv->bmv_count - 1;
        if (nex <= 0)
                return XFS_ERROR(EINVAL);

Signed-off-by Eric Sandeen <[email protected]>