[PATCH 1/2, RFC] xfsprogs: check fs sector size in platform_findsizes()

[Eric Sandeen]

Try the xfs geometry ioctl if the mkfs target resides
in a file; this gives us the equivalent of a device
sector size.

This does, however, emit a warning if the target file
exists on a non-XFS filesystem, and that might not be super.

Signed-off-by: Eric Sandeen <sandeen at redhat.com>
---

diff --git a/libxfs/linux.c b/libxfs/linux.c
index 2e07d54..d66a90f 100644
--- a/libxfs/linux.c
+++ b/libxfs/linux.c
@@ -141,10 +141,19 @@ platform_findsizes(char *path, int fd, long long *sz, int *bsz)
 		exit(1);
 	}
 	if ((st.st_mode & S_IFMT) == S_IFREG) {
+		struct xfs_fsop_geom_v1 geom = { 0 };
+
 		*sz = (long long)(st.st_size >> 9);
-		*bsz = BBSIZE;
-		if (BBSIZE > max_block_alignment)
-			max_block_alignment = BBSIZE;
+		if (ioctl(fd, XFS_IOC_FSGEOMETRY_V1, &geom) < 0) {
+			fprintf(stderr, _("Cannot get host filesystem geometry.\n"
+	"mkfs may fail if there is a sector size mismatch between\n"
+	"the image and the host filesystem.\n"));
+			*bsz = BBSIZE;
+		} else
+			*bsz = geom.sectsize;
+
+		if (*bsz > max_block_alignment)
+			max_block_alignment = *bsz;
 		return;
 	}