Make -mount and -xdev do different things

POSIX now says -mount should skip the whole mount point, while -xdev
should only skip its descendents.

C.f. http://austingroupbugs.net/view.php?id=1133
C.f. https://savannah.gnu.org/bugs/?42318
C.f. https://savannah.gnu.org/bugs/?54745

6 files changed, 71 insertions, 34 deletions

diff --git a/bfs.1 b/bfs.1
index 3f6ad50..277aeb7 100644
--- a/bfs.1
+++ b/bfs.1
@@ -244,13 +244,12 @@ detects that the file tree is modified during the search (default:
 Ignore files deeper/shallower than
 .IR N .
 .RE
-.PP
+.TP
 .B \-mount
-.br
+Skip mount points entirely.
+.TP
 .B \-xdev
-.RS
 Don't descend into other mount points.
-.RE
 .TP
 .B \-noleaf
 Ignored; for compatibility with GNU find.
diff --git a/bftw.c b/bftw.c
index 444310c..370ab12 100644
--- a/bftw.c
+++ b/bftw.c
@@ -901,7 +901,7 @@ static bool bftw_need_stat(const struct bftw_state *state) {
 	}
 
 	if (ftwbuf->typeflag == BFTW_DIR) {
-		if (state->flags & (BFTW_DETECT_CYCLES | BFTW_XDEV)) {
+		if (state->flags & (BFTW_DETECT_CYCLES | BFTW_MOUNT | BFTW_XDEV)) {
 			return true;
 		}
 #if __linux__
@@ -1041,6 +1041,23 @@ static void bftw_init_ftwbuf(struct bftw_state *state, enum bftw_visit visit) {
 	}
 }
 
+/** Check if the current file is a mount point. */
+static bool bftw_is_mount(struct bftw_state *state, const char *name) {
+	const struct bftw_file *file = state->file;
+	if (!file) {
+		return false;
+	}
+
+	const struct bftw_file *parent = name ? file : file->parent;
+	if (!parent) {
+		return false;
+	}
+
+	const struct BFTW *ftwbuf = &state->ftwbuf;
+	const struct bfs_stat *statbuf = bftw_stat(ftwbuf, ftwbuf->stat_flags);
+	return statbuf && statbuf->dev != parent->dev;
+}
+
 /** Fill file identity information from an ftwbuf. */
 static void bftw_fill_id(struct bftw_file *file, const struct BFTW *ftwbuf) {
 	const struct bfs_stat *statbuf = ftwbuf->stat_cache.buf;
@@ -1071,6 +1088,10 @@ static enum bftw_action bftw_visit(struct bftw_state *state, const char *name, e
 		return BFTW_STOP;
 	}
 
+	if ((state->flags & BFTW_MOUNT) && bftw_is_mount(state, name)) {
+		return BFTW_PRUNE;
+	}
+
 	enum bftw_action ret = state->callback(ftwbuf, state->ptr);
 	switch (ret) {
 	case BFTW_CONTINUE:
@@ -1088,19 +1109,9 @@ static enum bftw_action bftw_visit(struct bftw_state *state, const char *name, e
 		goto done;
 	}
 
-	if (state->flags & BFTW_XDEV) {
-		const struct bftw_file *parent = state->file;
-		if (parent && !name) {
-			parent = parent->parent;
-		}
-
-		if (parent) {
-			const struct bfs_stat *statbuf = bftw_stat(ftwbuf, ftwbuf->stat_flags);
-			if (statbuf && statbuf->dev != parent->dev) {
-				ret = BFTW_PRUNE;
-				goto done;
-			}
-		}
+	if ((state->flags & BFTW_XDEV) && bftw_is_mount(state, name)) {
+		ret = BFTW_PRUNE;
+		goto done;
 	}
 
 done:
diff --git a/bftw.h b/bftw.h
index 573c5a9..06fdedb 100644
--- a/bftw.h
+++ b/bftw.h
@@ -184,8 +184,10 @@ enum bftw_flags {
 	BFTW_LOGICAL       = 1 << 4,
 	/** Detect directory cycles. */
 	BFTW_DETECT_CYCLES = 1 << 5,
-	/** Stay on the same filesystem. */
-	BFTW_XDEV          = 1 << 6,
+	/** Skip mount points and their descendents. */
+	BFTW_MOUNT         = 1 << 6,
+	/** Skip the descendents of mount points. */
+	BFTW_XDEV          = 1 << 7,
 };
 
 /**
diff --git a/eval.c b/eval.c
index d89e62a..e2690c0 100644
--- a/eval.c
+++ b/eval.c
@@ -1300,6 +1300,7 @@ static void dump_bftw_flags(enum bftw_flags flags) {
 	DEBUG_FLAG(flags, BFTW_COMFOLLOW);
 	DEBUG_FLAG(flags, BFTW_LOGICAL);
 	DEBUG_FLAG(flags, BFTW_DETECT_CYCLES);
+	DEBUG_FLAG(flags, BFTW_MOUNT);
 	DEBUG_FLAG(flags, BFTW_XDEV);
 
 	assert(!flags);
diff --git a/parse.c b/parse.c
index fbc987c..70cf13d 100644
--- a/parse.c
+++ b/parse.c
@@ -346,6 +346,10 @@ struct parser_state {
 	const char *depth_arg;
 	/** A "-prune"-type argument if any. */
 	const char *prune_arg;
+	/** A "-mount"-type argument if any. */
+	const char *mount_arg;
+	/** An "-xdev"-type argument if any. */
+	const char *xdev_arg;
 
 	/** The current time. */
 	struct timespec now;
@@ -1546,10 +1550,11 @@ static struct expr *parse_ls(struct parser_state *state, int arg1, int arg2) {
 }
 
 /**
- * Parse -mount, -xdev.
+ * Parse -mount.
  */
 static struct expr *parse_mount(struct parser_state *state, int arg1, int arg2) {
-	state->cmdline->flags |= BFTW_XDEV;
+	state->cmdline->flags |= BFTW_MOUNT;
+	state->mount_arg = state->argv[0];
 	return parse_nullary_option(state);
 }
 
@@ -2409,6 +2414,15 @@ static struct expr *parse_xattr(struct parser_state *state, int arg1, int arg2)
 }
 
 /**
+ * Parse -xdev.
+ */
+static struct expr *parse_xdev(struct parser_state *state, int arg1, int arg2) {
+	state->cmdline->flags |= BFTW_XDEV;
+	state->xdev_arg = state->argv[0];
+	return parse_nullary_option(state);
+}
+
+/**
  * Launch a pager for the help output.
  */
 static CFILE *launch_pager(pid_t *pid, CFILE *cout) {
@@ -2594,6 +2608,7 @@ static struct expr *parse_help(struct parser_state *state, int arg1, int arg2) {
 	cfprintf(cout, "  ${blu}-mindepth${rs} ${bld}N${rs}\n");
 	cfprintf(cout, "      Ignore files deeper/shallower than ${bld}N${rs}\n");
 	cfprintf(cout, "  ${blu}-mount${rs}\n");
+	cfprintf(cout, "      Skip mount points entirely\n");
 	cfprintf(cout, "  ${blu}-xdev${rs}\n");
 	cfprintf(cout, "      Don't descend into other mount points\n");
 	cfprintf(cout, "  ${blu}-noleaf${rs}\n");
@@ -2888,9 +2903,9 @@ static const struct table_entry parse_table[] = {
 	{"-warn", parse_warn, true},
 	{"-wholename", parse_path, false},
 	{"-writable", parse_access, W_OK},
-	{"-x", parse_mount},
+	{"-x", parse_xdev},
 	{"-xattr", parse_xattr},
-	{"-xdev", parse_mount},
+	{"-xdev", parse_xdev},
 	{"-xtype", parse_type, true},
 	{0},
 };
@@ -3183,17 +3198,23 @@ static struct expr *parse_whole_expr(struct parser_state *state) {
 		}
 	}
 
-	if (state->warn && state->depth_arg && state->prune_arg) {
-		parse_warning(state, "%s does not work in the presence of %s.\n", state->prune_arg, state->depth_arg);
+	if (state->warn) {
+		if (state->mount_arg && state->xdev_arg) {
+			parse_warning(state, "%s is redundant in the presence of %s.\n\n", state->xdev_arg, state->mount_arg);
+		}
+
+		if (state->depth_arg && state->prune_arg) {
+			parse_warning(state, "%s does not work in the presence of %s.\n", state->prune_arg, state->depth_arg);
 
-		if (state->interactive) {
-			fprintf(stderr, "Do you want to continue? ");
-			if (ynprompt() == 0) {
-				goto fail;
+			if (state->interactive) {
+				fprintf(stderr, "Do you want to continue? ");
+				if (ynprompt() == 0) {
+					goto fail;
+				}
 			}
-		}
 
-		fprintf(stderr, "\n");
+			fprintf(stderr, "\n");
+		}
 	}
 
 	return expr;
@@ -3275,8 +3296,10 @@ void dump_cmdline(const struct cmdline *cmdline, bool verbose) {
 	if (cmdline->ignore_races) {
 		cfprintf(cerr, "${blu}-ignore_readdir_race${rs} ");
 	}
-	if (cmdline->flags & BFTW_XDEV) {
+	if (cmdline->flags & BFTW_MOUNT) {
 		cfprintf(cerr, "${blu}-mount${rs} ");
+	} else if (cmdline->flags & BFTW_XDEV) {
+		cfprintf(cerr, "${blu}-xdev{rs} ");
 	}
 	if (cmdline->mindepth != 0) {
 		cfprintf(cerr, "${blu}-mindepth${rs} ${bld}%d${rs} ", cmdline->mindepth);
@@ -3411,6 +3434,8 @@ struct cmdline *parse_cmdline(int argc, char *argv[]) {
 		.last_arg = NULL,
 		.depth_arg = NULL,
 		.prune_arg = NULL,
+		.mount_arg = NULL,
+		.xdev_arg = NULL,
 	};
 
 	if (strcmp(xbasename(state.command), "find") == 0) {
diff --git a/tests/test_mount.out b/tests/test_mount.out
index 005bdcf..2425675 100644
--- a/tests/test_mount.out
+++ b/tests/test_mount.out
@@ -1,4 +1,3 @@
 scratch
 scratch/foo
-scratch/mnt
 scratch/foo/bar