btrfs-progs: mkfs: print which compression algos are compiled in

The compression support is optional, eg. also in 'btrfs-restore', so
print the support in help text.

usage: mkfs.btrfs [options] <dev> [<dev...>]

...
    --compress ALGO[:LEVEL]   compress files by algorithm and level, ALGO can be 'no' (default), zstd, lzo, zlib
                              Built-in:
                              - ZSTD: yes
                              - LZO: yes
                              - ZLIB: yes
...

Signed-off-by: David Sterba <[email protected]>

Author: kdave

Diff for: Documentation/mkfs.btrfs.rst

@@ -164,6 +164,10 @@ OPTIONS
         they would be larger than the uncompressed versions, and will set file attribute
         *NOCOMPRESS* if its beginning is found to be incompressible.
 
+        .. note::
+                The support for ZSTD and LZO is a compile-time option, please check
+                the output of :command:`mkfs.btrfs --help` for the actual support.
+
 -u|--subvol <type>:<subdir>
         Specify that *subdir* is to be created as a subvolume rather than a regular
         directory.  The option *--rootdir* must also be specified, and *subdir* must be an

Diff for: mkfs/main.c

@@ -442,6 +442,18 @@ static const char * const mkfs_usage[] = {
 	OPTLINE("-b|--byte-count SIZE", "set size of each device to SIZE (filesystem size is sum of all device sizes)"),
 	OPTLINE("-r|--rootdir DIR", "copy files from DIR to the image root directory"),
 	OPTLINE("--compress ALGO[:LEVEL]", "compress files by algorithm and level, ALGO can be 'no' (default), zstd, lzo, zlib"),
+	OPTLINE("", "Built-in:"),
+#if COMPRESSION_ZSTD
+	OPTLINE("", "- ZSTD: yes"),
+#else
+	OPTLINE("", "- ZSTD: no"),
+#endif
+#if COMPRESSION_LZO
+	OPTLINE("", "- LZO: yes"),
+#else
+	OPTLINE("", "- LZO: no"),
+#endif
+	OPTLINE("", "- ZLIB: yes"),
 	OPTLINE("-u|--subvol TYPE:SUBDIR", "create SUBDIR as subvolume rather than normal directory, can be specified multiple times"),
 	OPTLINE("--shrink", "(with --rootdir) shrink the filled filesystem to minimal size"),
 	OPTLINE("-K|--nodiscard", "do not perform whole device TRIM"),