mkfs-b: Map block size to cluster size for VFAT and NTFS partitions (RHBZ#599464).

This also adds a regression test for VFAT and (conditionally)
NTFS filesystems.

2 files changed, 51 insertions, 7 deletions

diff --git a/daemon/mkfs.c b/daemon/mkfs.c
index 2c3a3cd9..ad3014c3 100644
--- a/daemon/mkfs.c
+++ b/daemon/mkfs.c
@@ -102,17 +102,46 @@ int
 do_mkfs_b (const char *fstype, int blocksize, const char *device)
 {
   const char *extra[2];
-  char blocksize_s[32];
+  char n[32];
 
   if (blocksize <= 0 || !is_power_of_2 (blocksize)) {
     reply_with_error ("block size must be > 0 and a power of 2");
     return -1;
   }
 
-  snprintf (blocksize_s, sizeof blocksize_s, "%d", blocksize);
-
-  extra[0] = "-b";
-  extra[1] = blocksize_s;
+  if (STREQ (fstype, "vfat") ||
+      STREQ (fstype, "msdos")) {
+    /* For VFAT map the blocksize into a cluster size.  However we
+     * have to determine the block device sector size in order to do
+     * this.
+     */
+    int sectorsize = do_blockdev_getss (device);
+    if (sectorsize == -1)
+      return -1;
+
+    int sectors_per_cluster = blocksize / sectorsize;
+    if (sectors_per_cluster < 1 || sectors_per_cluster > 128) {
+      reply_with_error ("unsupported cluster size for %s filesystem (requested cluster size = %d, sector size = %d, trying sectors per cluster = %d)",
+                        fstype, blocksize, sectorsize, sectors_per_cluster);
+      return -1;
+    }
+
+    snprintf (n, sizeof n, "%d", sectors_per_cluster);
+    extra[0] = "-s";
+    extra[1] = n;
+  }
+  else if (STREQ (fstype, "ntfs")) {
+    /* For NTFS map the blocksize into a cluster size. */
+    snprintf (n, sizeof n, "%d", blocksize);
+    extra[0] = "-c";
+    extra[1] = n;
+  }
+  else {
+    /* For all other filesystem types, try the -b option. */
+    snprintf (n, sizeof n, "%d", blocksize);
+    extra[0] = "-b";
+    extra[1] = n;
+  }
 
   return mkfs (fstype, device, extra, 2);
 }
diff --git a/src/generator.ml b/src/generator.ml
index 4d74cb00..ec6123aa 100755
--- a/src/generator.ml
+++ b/src/generator.ml
@@ -3732,13 +3732,28 @@ and C<guestfs_setcon>");
        ["mkfs_b"; "ext2"; "4096"; "/dev/sda1"];
        ["mount_options"; ""; "/dev/sda1"; "/"];
        ["write"; "/new"; "new file contents"];
-       ["cat"; "/new"]], "new file contents")],
+       ["cat"; "/new"]], "new file contents");
+    InitEmpty, Always, TestRun (
+      [["part_disk"; "/dev/sda"; "mbr"];
+       ["mkfs_b"; "vfat"; "32768"; "/dev/sda1"]]);
+    InitEmpty, Always, TestLastFail (
+      [["part_disk"; "/dev/sda"; "mbr"];
+       ["mkfs_b"; "vfat"; "32769"; "/dev/sda1"]]);
+    InitEmpty, Always, TestLastFail (
+      [["part_disk"; "/dev/sda"; "mbr"];
+       ["mkfs_b"; "vfat"; "33280"; "/dev/sda1"]]);
+    InitEmpty, IfAvailable "ntfsprogs", TestRun (
+      [["part_disk"; "/dev/sda"; "mbr"];
+       ["mkfs_b"; "ntfs"; "32768"; "/dev/sda1"]])],
    "make a filesystem with block size",
    "\
 This call is similar to C<guestfs_mkfs>, but it allows you to
 control the block size of the resulting filesystem.  Supported
 block sizes depend on the filesystem type, but typically they
-are C<1024>, C<2048> or C<4096> only.");
+are C<1024>, C<2048> or C<4096> only.
+
+For VFAT and NTFS the C<blocksize> parameter is treated as
+the requested cluster size.");
 
   ("mke2journal", (RErr, [Int "blocksize"; Device "device"]), 188, [],
    [InitEmpty, Always, TestOutput (