blkid: add pretty output, document -L incompatibility with e2fsprogs

... sad story, I have temporary disabled pretty-output code
in very early version of blkid.c in u-l-ng. (It was also in
time when pretty-output was very new feature in e2fsprogs.)

Unfortunately, the -L option (shortcut to "-o list") in u-l-ng version
was reused for for any other functionality few months later.... this
stupid thing was released in u-l-ng 2.15 and 2.16 without any negative
feedback from users.

It means the blkid from u-l-ng is not backwardly compatible with
the original version from e2fsprogs. The -L option has a different
meaning there.

I'm sorry about this bug...

This patch:

  * enable pretty-output (-o line)
  * add a note about incompatibility between u-l-ng and e2fsprogs
    to blkid.8 man page

Signed-off-by: Karel Zak <kzak@redhat.com>

misc-utils/Makefile.am

@@ -35,6 +35,7 @@ endif
 if BUILD_LIBBLKID
 sbin_PROGRAMS += blkid findfs wipefs
 dist_man_MANS += blkid.8 findfs.8 wipefs.8
+blkid_SOURCES = blkid.c $(top_srcdir)/lib/ismounted.c
 blkid_LDADD = $(ul_libblkid_la)
 blkid_CFLAGS = -I$(ul_libblkid_srcdir)
 findfs_LDADD = $(ul_libblkid_la)

misc-utils/blkid.8

@@ -96,7 +96,13 @@ Look up one device that uses the label (same as: -l -o device -t
 LABEL=<label>).  This look up method is able to reliable use /dev/disk/by-label
 udev symlinks (depends on setting in /etc/blkid.conf). Avoid to use the
 symlinks directly. It is not reliable to use the symlinks without verification.
-The \fB-L\fR option is portable and works on systems with and without udev.
+The \fB-L\fR option works on systems with and without udev.
+
+Unfortunately, the original
+.B blkid(8)
+from e2fsprogs use the \fB-L\fR option as a
+synonym to the \fB-o list\fR option. For better portability use "-l -o device
+-t LABEL=<label>" and "-o list" in your scripts rather than -L option.
 .TP
 .B \-u " list "
 Restrict probing functions to defined (comma separated) list of "usage" types.
@@ -130,10 +136,12 @@ print all tags (the default)
 print the value of the tags
 .TP
 .B list
-print the devices in a user-friendly format
+print the devices in a user-friendly format, this output format is unsupported
+for low-level probing (\fB-p\fR)
 .TP
 .B device
-print the device name only
+print the device name only, this output format is always enabled for \fB-L\fR
+and \fB-U\fR options
 .TP
 .B udev
 vol_id compatible mode; usable in udev rules

misc-utils/blkid.c

@@ -40,6 +40,8 @@ extern int optind;
 
 #include <blkid.h>
 
+#include "ismounted.h"
+
 const char *progname = "blkid";
 
 static void print_version(FILE *out)
@@ -186,16 +188,12 @@ static void pretty_print_line(const char *device, const char *fs_type,
 
 static void pretty_print_dev(blkid_dev dev)
 {
-	fprintf(stderr, "pretty print not implemented yet\n");
-
-#ifdef NOT_IMPLEMENTED
 	blkid_tag_iterate	iter;
 	const char		*type, *value, *devname;
 	const char		*uuid = "", *fs_type = "", *label = "";
-	char			*cp;
 	int			len, mount_flags;
 	char			mtpt[80];
-	errcode_t		retval;
+	int			retval;
 
 	if (dev == NULL) {
 		pretty_print_line("device", "fs_type", "label",
@@ -224,20 +222,18 @@ static void pretty_print_dev(blkid_dev dev)
 
 	/* Get the mount point */
 	mtpt[0] = 0;
-	retval = ext2fs_check_mount_point(devname, &mount_flags,
-					  mtpt, sizeof(mtpt));
+	retval = check_mount_point(devname, &mount_flags, mtpt, sizeof(mtpt));
 	if (retval == 0) {
-		if (mount_flags & EXT2_MF_MOUNTED) {
+		if (mount_flags & MF_MOUNTED) {
 			if (!mtpt[0])
 				strcpy(mtpt, "(mounted, mtpt unknown)");
-		} else if (mount_flags & EXT2_MF_BUSY)
+		} else if (mount_flags & MF_BUSY)
 			strcpy(mtpt, "(in use)");
 		else
 			strcpy(mtpt, "(not mounted)");
 	}
 
 	pretty_print_line(devname, fs_type, label, mtpt, uuid);
-#endif
 }
 
 static void print_udev_format(const char *name, const char *value, size_t sz)
@@ -544,8 +540,14 @@ int main(int argc, char **argv)
 	}
 	err = 2;
 
-	if (output_format & OUTPUT_PRETTY_LIST)
+	if (eval == 0 && output_format & OUTPUT_PRETTY_LIST) {
+		if (lowprobe) {
+			fprintf(stderr, "The low-level probing mode does not "
+					"support 'list' output format\n");
+			exit(4);
+		}
 		pretty_print_dev(NULL);
+	}
 
 	if (lowprobe) {
 		/*
@@ -554,7 +556,8 @@ int main(int argc, char **argv)
 		blkid_probe pr;
 
 		if (!numdev) {
-			fprintf(stderr, "The low-probe option requires a device\n");
+			fprintf(stderr, "The low-level probing mode "
+					"requires a device\n");
 			exit(4);
 		}
 		pr = blkid_new_probe();