livemedia-creator: Make sure the rootfs.img can be compressed

Use 4k blocks for the ext4 filesystem. Run fsck on the filesystem to
make sure deleted blocks are actually zeroed, and pass -Xbcj to
mksquashfs.

4k blocks and -Xbcj decreases the size by 2-6% depending on the
filesystem size. Zeroing the blocks of the ext4 fs improves things
dramatically. The problem is that DNF downloads the rpms before
installing them. In addition to forcing us to use a larger filesystem
than we would like it leaves data that is difficult to compress on the
image. The downloaded files are removed, but need to be zeroed out so
that mksquashfs can compress it.

src/pylorax/imgutils.py

@@ -437,7 +437,7 @@ def mkdosimg(rootdir, outfile, size=None, label="", mountargs="shortname=winnt,u
 def mkext4img(rootdir, outfile, size=None, label="", mountargs="", graft=None):
     graft = graft or {}
     mkfsimage("ext4", rootdir, outfile, size, mountargs=mountargs,
-              mkfsargs=["-L", label, "-b", "1024", "-m", "0"], graft=graft)
+              mkfsargs=["-L", label, "-b", "4096", "-m", "0"], graft=graft)
 
 def mkbtrfsimg(rootdir, outfile, size=None, label="", mountargs="", graft=None):
     graft = graft or {}

src/sbin/livemedia-creator

@@ -893,7 +893,7 @@ def virt_install(opts, install_log, disk_img, disk_size):
         shutil.rmtree(vagrant_dir)
 
 
-def make_squashfs(disk_img, work_dir, compression="xz"):
+def make_squashfs(disk_img, work_dir, compression="xz", compressargs=None):
     """
     Create a squashfs image of an unpartitioned filesystem disk image
 
@@ -904,6 +904,11 @@ def make_squashfs(disk_img, work_dir, compression="xz"):
     Take disk_img and put it into LiveOS/rootfs.img and squashfs this
     tree into work_dir+images/install.img
     """
+    # Make sure free blocks are actually zeroed so it will compress
+    rc = execWithRedirect("/usr/sbin/fsck.ext4", ["-y", "-f", "-E", "discard", disk_img])
+    if rc != 0:
+        log.warning("Problem zeroing free blocks of %s", disk_img)
+
     liveos_dir = joinpaths(work_dir, "runtime/LiveOS")
     os.makedirs(liveos_dir)
     os.makedirs(os.path.dirname(joinpaths(work_dir, RUNTIME)))
@@ -913,7 +918,7 @@ def make_squashfs(disk_img, work_dir, compression="xz"):
         shutil.copy2(disk_img, joinpaths(liveos_dir, "rootfs.img"))
 
     mksquashfs(joinpaths(work_dir, "runtime"),
-               joinpaths(work_dir, RUNTIME), compression)
+               joinpaths(work_dir, RUNTIME), compression, compressargs)
     remove(joinpaths(work_dir, "runtime"))
 
 
@@ -995,6 +1000,11 @@ def make_live_images(opts, work_dir, root_dir, rootfs_image=None, size=None):
     os.makedirs(liveos_dir)
 
     if rootfs_image:
+        # Make sure free blocks are actually zeroed so it will compress
+        rc = execWithRedirect("/usr/sbin/fsck.ext4", ["-y", "-f", "-E", "discard", rootfs_image])
+        if rc != 0:
+            log.warning("Problem zeroing free blocks of %s", rootfs_image)
+
         rc = execWithRedirect("/bin/ln", [rootfs_image, joinpaths(liveos_dir, "rootfs.img")])
         if rc != 0:
             shutil.copy2(rootfs_image, joinpaths(liveos_dir, "rootfs.img"))
@@ -1386,7 +1396,15 @@ def main():
                 # Create iso from a filesystem image
                 disk_img = opts.fs_image or disk_img
 
-                make_squashfs(disk_img, work_dir)
+                compression = opts.compression or "xz"
+                if not opts.compress_args:
+                    arch = ArchData(opts.arch or os.uname().machine)
+                    if arch.bcj:
+                        compressargs = ["-Xbcj", arch.bcj]
+                    else:
+                        log.info("no BCJ filter for arch %s", arch.basearch)
+
+                make_squashfs(disk_img, work_dir, compression, compressargs)
                 with Mount(disk_img, opts="loop") as mount_dir:
                     result_dir = make_livecd(opts, mount_dir, work_dir)
             else: