[PATCH, RFC] mkfs.xfs: go into multidisk mode when geometry is on cmdline

[Eric Sandeen <sandeen@sandeen.net>]

In the course of some other investigations, I found that 
calc_default_ag_geometry() doesn't go into "multidisk" mode
unless stripe geometry is *detected* (i.e. by the blkid routines).

Specifying a geometry on the cmdline is *not* sufficient, because
we test (ft.dsunit | ft.dswidth) which are not set by the cmdline
options.

If we move the AG calculations to after we have set dsunit & dswdith,
then we'll pick up either cmdline-specified or blkid-detected
geometry, and go into "multidisk" mode for AG size/count
calculations in both cases.

So now for a ~5T fs, for example, we'd make several more
AGs:

# truncate --size=5t fsfile
# mkfs.xfs -N -d su=128k,sw=8 fsfile | grep agcount
meta-data=fsfile                 isize=256    agcount=5, agsize=268435424 blks
# mkfs/mkfs.xfs -N -d su=128k,sw=8 fsfile | grep agcount
meta-data=fsfile                 isize=256    agcount=32, agsize=41943008 blks

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

TBH, though, is there ever any value in treating a very large
fs as "!multidisk?"  When would we ever want to pretend that
a 16T filesystem doesn't have a lot of spindles behind it?

diff --git a/mkfs/xfs_mkfs.c b/mkfs/xfs_mkfs.c
index be931e3..42a7b5b 100644
--- a/mkfs/xfs_mkfs.c
+++ b/mkfs/xfs_mkfs.c
@@ -2090,25 +2091,6 @@ _("size %s specified for log subvolume is too large, maximum is %lld blocks\n"),
 		nbmblocks = 0;
 	}
 
-	if (dasize) {		/* User-specified AG size */
-		/*
-		 * Check specified agsize is a multiple of blocksize.
-		 */
-		if (agsize % blocksize) {
-			fprintf(stderr,
-		_("agsize (%lld) not a multiple of fs blk size (%d)\n"),
-				(long long)agsize, blocksize);
-			usage();
-		}
-		agsize /= blocksize;
-		agcount = dblocks / agsize + (dblocks % agsize != 0);
-
-	} else if (daflag)	/* User-specified AG count */
-		agsize = dblocks / agcount + (dblocks % agcount != 0);
-	else
-		calc_default_ag_geometry(blocklog, dblocks,
-				ft.dsunit | ft.dswidth, &agsize, &agcount);
-
 	if (!nodsflag) {
 		if (dsunit) {
 			if (ft.dsunit && ft.dsunit != dsunit) {
@@ -2132,6 +2114,25 @@ _("size %s specified for log subvolume is too large, maximum is %lld blocks\n"),
 		}
 	} /* else dsunit & dswidth can't be set if nodsflag is set */
 
+	if (dasize) {		/* User-specified AG size */
+		/*
+		 * Check specified agsize is a multiple of blocksize.
+		 */
+		if (agsize % blocksize) {
+			fprintf(stderr,
+		_("agsize (%lld) not a multiple of fs blk size (%d)\n"),
+				(long long)agsize, blocksize);
+			usage();
+		}
+		agsize /= blocksize;
+		agcount = dblocks / agsize + (dblocks % agsize != 0);
+
+	} else if (daflag)	/* User-specified AG count */
+		agsize = dblocks / agcount + (dblocks % agcount != 0);
+	else
+		calc_default_ag_geometry(blocklog, dblocks,
+				dsunit | dswidth, &agsize, &agcount);
+
 	/*
 	 * If dsunit is a multiple of fs blocksize, then check that is a
 	 * multiple of the agsize too

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