[Bug 1785499] Re: Make squashfs-tools in Xenial in sync with Bionic and Cosmic

Wed Aug 8 22:56:25 UTC 2018

I confirmed that I can create a squashfs larger than 2GB (used 2.1GB),
then append a file to it (used a 50MB file) and the resulting squashfs
can be unpacked just fine.

```
root at xenial-32:~# dd if=/dev/urandom of=big bs=10M count=210
210+0 records in
210+0 records out
2202009600 bytes (2.2 GB, 2.1 GiB) copied, 147.973 s, 14.9 MB/s
root at xenial-32:~# mksquashfs big big.squashfs
Parallel mksquashfs: Using 8 processors
Creating 4.0 filesystem on big.squashfs, block size 131072.
[==========================================================================================================================================/] 16800/16800 100%

Exportable Squashfs 4.0 filesystem, gzip compressed, data block size 131072
	compressed data, compressed metadata, compressed fragments, compressed xattrs
	duplicates are removed
Filesystem size 2150400.52 Kbytes (2100.00 Mbytes)
	100.00% of uncompressed filesystem size (2150465.88 Kbytes)
Inode table size 353 bytes (0.34 Kbytes)
	0.52% of uncompressed inode table size (67282 bytes)
Directory table size 21 bytes (0.02 Kbytes)
	84.00% of uncompressed directory table size (25 bytes)
Number of duplicate files found 0
Number of inodes 2
Number of files 1
Number of fragments 1
Number of symbolic links  0
Number of device nodes 0
Number of fifo nodes 0
Number of socket nodes 0
Number of directories 1
Number of ids (unique uids + gids) 1
Number of uids 1
	root (0)
Number of gids 1
	root (0)
root at xenial-32:~# dd if=/dev/urandom of=small bs=10M count=5
5+0 records in
5+0 records out
52428800 bytes (52 MB, 50 MiB) copied, 3.5235 s, 14.9 MB/s
root at xenial-32:~# mksquashfs small big.squashfs 
Found a valid exportable SQUASHFS superblock on big.squashfs.
	Compression used gzip
	Inodes are compressed
	Data is compressed
	Fragments are compressed
	Xattrs are compressed
	Fragments are present in the filesystem
	Always-use-fragments option is not specified
	Duplicates are removed
	Xattrs are stored
	Filesystem size 2150400.52 Kbytes (2100.00 Mbytes)
	Block size 131072
	Number of fragments 1
	Number of inodes 2
	Number of ids 1

Parallel mksquashfs: Using 8 processors
Scanning existing filesystem...
Read existing filesystem, 1 inodes scanned
Appending to existing 4.0 filesystem on big.squashfs, block size 131072
All -b, -noI, -noD, -noF, -noX, no-duplicates, no-fragments, -always-use-fragments,
-exportable and -comp options ignored

If appending is not wanted, please re-run with -noappend specified!

Recovery file "squashfs_recovery_big.squashfs_256" written
If Mksquashfs aborts abnormally (i.e. power failure), run
mksquashfs dummy big.squashfs -recover squashfs_recovery_big.squashfs_256
to restore filesystem

[==============================================================================================================================================-]
400/400 100%

Exportable Squashfs 4.0 filesystem, gzip compressed, data block size 131072
	compressed data, compressed metadata, compressed fragments, compressed xattrs
	duplicates are removed
Filesystem size 2201600.58 Kbytes (2150.00 Mbytes)
	100.00% of uncompressed filesystem size (2201667.49 Kbytes)
Inode table size 388 bytes (0.38 Kbytes)
	0.56% of uncompressed inode table size (68898 bytes)
Directory table size 40 bytes (0.04 Kbytes)
	80.00% of uncompressed directory table size (50 bytes)
Number of duplicate files found 0
Number of inodes 3
Number of files 2
Number of fragments 1
Number of symbolic links  0
Number of device nodes 0
Number of fifo nodes 0
Number of socket nodes 0
Number of directories 1
Number of ids (unique uids + gids) 1
Number of uids 1
	root (0)
Number of gids 1
	root (0)
root at xenial-32:~# ls
big  big.squashfs  small
root at xenial-32:~# mkdir a
root at xenial-32:~# cd a
root at xenial-32:~/a# unsquashfs ../big.squashfs 
Parallel unsquashfs: Using 8 processors
2 inodes (17200 blocks) to write

[==========================================================================================================================================|]
17200/17200 100%

created 2 files
created 1 directories
created 0 symlinks
created 0 devices
created 0 fifos
```

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https://bugs.launchpad.net/bugs/1785499

Title:
  Make squashfs-tools in Xenial in sync with Bionic and Cosmic

Status in squashfs-tools package in Ubuntu:
  Fix Released
Status in squashfs-tools source package in Xenial:
  Fix Committed

Bug description:
  squashfs-tools upstream hasn't changed in a while but a number of
  bugfixes are applied through packaging in Debian and Ubuntu.

  The bionic and cosmic versions right now are identical but xenial is
  missing a few fixes which is a problem for the LXD snap among other
  things.

  Looking at debian/series/patches, the fixes currently missing in the xenial version are:
   - 0007-fix-2GB-limit-in-mksquashfs.patch
   - 0008-preserve_file_capabilities.patch

  I'll attach test cases for both of those below and then will prepare
  an SRU that effectively makes the source package identical to what we
  have in bionic, minus the different changelog.

  This should be pretty safe considering both Ubuntu and Debian have
  been shipping those two patches for a while and the fs caps one is
  going to be pretty important moving forward as we're discussing having
  Ubuntu ship with fscaps by default.

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