Update usage and manpage for mkcomposefs

Signed-off-by: Alexander Larsson <[email protected]>

man/mkcomposefs.md

@@ -9,11 +9,13 @@ mkcomposefs - create a composefs filesystem image
 
 # DESCRIPTION
 
-The composefs project uses EROFS to store metadata, and a distinct
-underlying backing store for regular files.
+The composefs project uses EROFS image file to store metadata, and one
+or more separate directories containing content-addressed backing data
+for regular files.
 
 **mkcomposefs** constructs the mountable "composefs image" using the
-source directory as input.
+source directory as input. It can also create the backing store
+directory.
 
 # OPTIONS
 
@@ -23,14 +25,37 @@ will be a mountable composefs image.
 
 **mkcomposefs** accepts the following options:
 
+
 **\-\-digest-store**=*PATH*
-:   This path will become a composefs "object store".  Non-empty regular files
-    in the *SOURCEDIR* will be copied (reflinked if possible) into this target
-    directory, named after their fsverity digest.
+:   This path will become a composefs "object store". Non-empty
+    regular files in the *SOURCEDIR* will be copied (reflinked if
+    possible) into this target directory, named after their fsverity
+    digest. If possible, the added files will have fs-verity enabled.
+
+    This directory should be passed to the basedir option when you
+    mount the image.
 
 **\-\-print-digest**
 :   Print the fsverity digest of the composefs metadata file.
 
+**\-\-print-digest-only**
+:   Print the fsverity digest of the composefs metadata file, but
+    don't write the image. If this is passed, the *IMAGE* argument should
+    be left out.
+
+**\-\-use-epoch**
+:   Use a zero time (unix epoch) as the modification time for all files.
+
+**\-\-skip-devices**
+:   Don't add device nodes to the image.
+
+**\-\-skip-xattrs**
+:   Don't add xattrs to files in the image.
+
+**\-\-user-xattrs**
+:   Only add xattrs with the "user." prefix to files in the image.
+
+
 # SEE ALSO
 
 - [composefs upstream](https://github.com/containers/composefs)

tools/mkcomposefs.c

@@ -308,9 +308,17 @@ static int fill_store(struct lcfs_node_s *node, const char *path,
 
 static void usage(const char *argv0)
 {
+	const char *bin = basename(argv0);
 	fprintf(stderr,
-		"usage: %s [--use-epoch] [--skip-xattrs] [--absolute] [--by-digest] [--digest-store=path] [--print-digest] [--print-digest-only] [--skip-devices] [--compute-digest] SOURCEDIR IMAGE\n",
-		argv0);
+		"Usage: %s [OPTIONS] SOURCEDIR IMAGE\n"
+		"Options:\n"
+		"  --digest-store=PATH   Store content files in this directory\n"
+		"  --use-epoch           Make all mtimes zero\n"
+		"  --skip-xattrs         Don't store file xattrs\n"
+		"  --user-xattrs         Only store user.* xattrs\n"
+		"  --print-digest        Print the digest of the image\n"
+		"  --print-digest-only   Print the digest of the image, don't write image\n",
+		bin);
 }
 
 #define OPT_SKIP_XATTRS 102