btrfs-progs: add quota-related info to usage messages

Extending usage messages with some info on the quota functionality:
     - The -i option of "subvol create" and "subvol snapshot" was not
documented
     - The -c option of "qgroup limit" is the default option
     - The "qouta rescan" command is not yet implemented, while it should be
       executed after enabling quota on a non-empty filesystem.

Signed-off-by: Koen De Wit <koen.de.wit@oracle.com>

cmds-qgroup.c

@@ -326,7 +326,8 @@ static const char * const cmd_qgroup_limit_usage[] = {
 	"btrfs qgroup limit [options] <size>|none [<qgroupid>] <path>",
 	"Limit the size of a subvolume quota group.",
 	"",
-	"-c   limit amount of data after compression",
+	"-c   limit amount of data after compression. This is the default,",
+	"     it is currently not possible to turn off this option.",
 	"-e   limit space exclusively assigned to this qgroup",
 	NULL
 };

cmds-quota.c

@@ -64,6 +64,9 @@ int quota_ctl(int cmd, int argc, char **argv)
 static const char * const cmd_quota_enable_usage[] = {
 	"btrfs quota enable <path>",
 	"Enable subvolume quota support for a filesystem.",
+	"Any data already present on the filesystem will not count towards",
+	"the space usage numbers. It is recommended to enable quota for a",
+	"filesystem before writing any data to it.",
 	NULL
 };
 
@@ -92,6 +95,7 @@ static int cmd_quota_disable(int argc, char **argv)
 static const char * const cmd_quota_rescan_usage[] = {
 	"btrfs quota rescan <path>",
 	"Rescan the subvolume for a changed quota setting.",
+	"Not yet implemented.",
 	NULL
 };
 

cmds-subvolume.c

@@ -61,10 +61,13 @@ static int test_isdir(char *path)
 }
 
 static const char * const cmd_subvol_create_usage[] = {
-	"btrfs subvolume create [<dest>/]<name>",
+	"btrfs subvolume create [-i <qgroupid>] [<dest>/]<name>",
 	"Create a subvolume",
 	"Create a subvolume <name> in <dest>.  If <dest> is not given",
 	"subvolume <name> will be created in the current directory.",
+	"",
+	"-i <qgroupid>  add the newly created subvolume to a qgroup. This",
+	"               option can be given multiple times.",
 	NULL
 };
 
@@ -481,11 +484,14 @@ out:
 
 static const char * const cmd_snapshot_usage[] = {
 	"btrfs subvolume snapshot [-r] <source> [<dest>/]<name>",
+	"btrfs subvolume snapshot [-r] [-i <qgroupid>] <source> [<dest>/]<name>",
 	"Create a snapshot of the subvolume",
 	"Create a writable/readonly snapshot of the subvolume <source> with",
 	"the name <name> in the <dest> directory",
 	"",
-	"-r     create a readonly snapshot",
+	"-r             create a readonly snapshot",
+	"-i <qgroupid>  add the newly created snapshot to a qgroup. This",
+	"               option can be given multiple times.",
 	NULL
 };