Give better error messages on database locking failures

This was noted when trying to perform an operation on a pacman database
on a read-only file system. Print the actual underlying errno string,
and only show the "you can remove" message if the lock file actually
exists.

Before:
    $ pacman -Su
    error: failed to init transaction (unable to lock database)
      if you're sure a package manager is not already
      running, you can remove /e/db.lck

After:
    $ pacman -Su
    error: failed to init transaction (unable to lock database)
    error: could not lock database: Read-only file system

Signed-off-by: Dan McGee <dan@archlinux.org>

1 files changed, 7 insertions, 3 deletions

diff --git a/src/pacman/util.c b/src/pacman/util.c
index 0b076d97..f7f8ecf5 100644
--- a/src/pacman/util.c
+++ b/src/pacman/util.c
@@ -69,9 +69,13 @@ void trans_init_error(void)
 	pm_printf(ALPM_LOG_ERROR, _("failed to init transaction (%s)\n"),
 			alpm_strerror(err));
 	if(err == ALPM_ERR_HANDLE_LOCK) {
-		fprintf(stderr, _("  if you're sure a package manager is not already\n"
-					"  running, you can remove %s\n"),
-				alpm_option_get_lockfile(config->handle));
+		const char *lockfile = alpm_option_get_lockfile(config->handle);
+		pm_printf(ALPM_LOG_ERROR, _("could not lock database: %s\n"),
+					strerror(errno));
+		if(access(lockfile, F_OK) == 0) {
+			fprintf(stderr, _("  if you're sure a package manager is not already\n"
+						"  running, you can remove %s\n"), lockfile);
+		}
 	}
 }