fish: New command 'sparse', like 'alloc' but to generate sparse files.

With sparse you can make sparse files, which is fun because you
can experiment with really large devices:

  ><fs> sparse /tmp/test.img 100G
  ><fs> run
  ><fs> sfdiskM /dev/vda ,
  ><fs> mkfs ext2 /dev/vda1    # very long pause here ...
  ><fs> mount /dev/vda1 /

To see the real (ie. allocated) size of the sparse file, use the du
command, eg:

  ><fs> !du -h /tmp/test.img
  1.6G -rw-rw-r-- 1 rjones rjones 100G 2009-11-04 17:40 /tmp/test.img

1 files changed, 54 insertions, 0 deletions

diff --git a/fish/alloc.c b/fish/alloc.c
index a7d115a9..e35c02f7 100644
--- a/fish/alloc.c
+++ b/fish/alloc.c
@@ -75,6 +75,60 @@ do_alloc (const char *cmd, int argc, char *argv[])
   return 0;
 }
 
+int
+do_sparse (const char *cmd, int argc, char *argv[])
+{
+  off_t size;
+  int fd;
+  char c = 0;
+
+  if (argc != 2) {
+    fprintf (stderr, _("use 'sparse file size' to create a sparse image\n"));
+    return -1;
+  }
+
+  if (parse_size (argv[1], &size) == -1)
+    return -1;
+
+  if (!guestfs_is_config (g)) {
+    fprintf (stderr, _("can't allocate or add disks after launching\n"));
+    return -1;
+  }
+
+  fd = open (argv[0], O_WRONLY|O_CREAT|O_NOCTTY|O_TRUNC, 0666);
+  if (fd == -1) {
+    perror (argv[0]);
+    return -1;
+  }
+
+  if (lseek (fd, size-1, SEEK_SET) == (off_t) -1) {
+    perror ("lseek");
+    close (fd);
+    unlink (argv[0]);
+    return -1;
+  }
+
+  if (write (fd, &c, 1) != 1) {
+    perror ("write");
+    close (fd);
+    unlink (argv[0]);
+    return -1;
+  }
+
+  if (close (fd) == -1) {
+    perror (argv[0]);
+    unlink (argv[0]);
+    return -1;
+  }
+
+  if (guestfs_add_drive (g, argv[0]) == -1) {
+    unlink (argv[0]);
+    return -1;
+  }
+
+  return 0;
+}
+
 static int
 parse_size (const char *str, off_t *size_rtn)
 {