[PATCH v2] xfs_scrub: don't use statvfs to collect filesystem summary counts

["Darrick J. Wong" <darrick.wong@oracle.com>]

From: Darrick J. Wong <darrick.wong@oracle.com>

The function scrub_scan_estimate_blocks naïvely uses the statvfs counts
to estimate the size and free blocks on the data volume.  Unfortunately,
it fails to account for the fact that statvfs can return the size and
free counts for the realtime volume if the root directory has the
rtinherit flag set, which leads to phase 7 reporting totally absurd
quantities.

Eric pointed out a further problem with statvfs, which is that the file
counts are clamped to the current user's project quota inode limits.
Therefore, we must not use statvfs for querying the filesystem summary
counts.

The XFS_IOC_FSCOUNTS ioctl returns all the data we need, so use that
instead.

Fixes: 604dd3345f35 ("xfs_scrub: filesystem counter collection functions")
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
v2: drop statvfs entirely
---
 scrub/fscounters.c |   27 ++++-----------------------
 1 file changed, 4 insertions(+), 23 deletions(-)

diff --git a/scrub/fscounters.c b/scrub/fscounters.c
index f9d64f8c008f..e9901fcdf6df 100644
--- a/scrub/fscounters.c
+++ b/scrub/fscounters.c
@@ -130,38 +130,19 @@ scrub_scan_estimate_blocks(
 	unsigned long long		*f_free)
 {
 	struct xfs_fsop_counts		fc;
-	struct xfs_fsop_resblks		rb;
-	struct statvfs			sfs;
 	int				error;
 
-	/* Grab the fstatvfs counters, since it has to report accurately. */
-	error = fstatvfs(ctx->mnt.fd, &sfs);
-	if (error)
-		return errno;
-
 	/* Fetch the filesystem counters. */
 	error = ioctl(ctx->mnt.fd, XFS_IOC_FSCOUNTS, &fc);
 	if (error)
 		return errno;
 
-	/*
-	 * XFS reserves some blocks to prevent hard ENOSPC, so add those
-	 * blocks back to the free data counts.
-	 */
-	error = ioctl(ctx->mnt.fd, XFS_IOC_GET_RESBLKS, &rb);
-	if (error)
-		return errno;
-
-	sfs.f_bfree += rb.resblks_avail;
-
-	*d_blocks = sfs.f_blocks;
-	if (ctx->mnt.fsgeom.logstart > 0)
-		*d_blocks += ctx->mnt.fsgeom.logblocks;
-	*d_bfree = sfs.f_bfree;
+	*d_blocks = ctx->mnt.fsgeom.datablocks;
+	*d_bfree = fc.freedata;
 	*r_blocks = ctx->mnt.fsgeom.rtblocks;
 	*r_bfree = fc.freertx;
-	*f_files = sfs.f_files;
-	*f_free = sfs.f_ffree;
+	*f_files = fc.allocino;
+	*f_free = fc.freeino;
 
 	return 0;
 }