bfstd: New {error,errno}_is_like() functions

We used to have is_nonexistence_error() to consistently treat ENOENT and
ENOTDIR the same.  Recently, we started considering EFAULT the same as
ENAMETOOLONG on DragonFly BSD to work around a kernel bug.  Unify both
of these behind a more generic interface.

6 files changed, 45 insertions, 35 deletions

diff --git a/src/bfstd.c b/src/bfstd.c
index c0e61cb..15e8667 100644
--- a/src/bfstd.c
+++ b/src/bfstd.c
@@ -36,8 +36,27 @@
 #  include <util.h>
 #endif
 
-bool is_nonexistence_error(int error) {
-	return error == ENOENT || errno == ENOTDIR;
+bool error_is_like(int error, int category) {
+	if (error == category) {
+		return true;
+	}
+
+	switch (category) {
+	case ENOENT:
+		return error == ENOTDIR;
+
+#if __DragonFly__
+	// https://twitter.com/tavianator/status/1742991411203485713
+	case ENAMETOOLONG:
+		return error == EFAULT;
+#endif
+	}
+
+	return false;
+}
+
+bool errno_is_like(int category) {
+	return error_is_like(errno, category);
 }
 
 char *xdirname(const char *path) {
diff --git a/src/bfstd.h b/src/bfstd.h
index 0fcb892..8953b9b 100644
--- a/src/bfstd.h
+++ b/src/bfstd.h
@@ -45,9 +45,23 @@
 // #include <errno.h>
 
 /**
- * Return whether an error code is due to a path not existing.
+ * Check if an error code is "like" another one.  For example, ENOTDIR is
+ * like ENOENT because they can both be triggered by non-existent paths.
+ *
+ * @param error
+ *         The error code to check.
+ * @param category
+ *         The category to test for.  Known categories include ENOENT and
+ *         ENAMETOOLONG.
+ * @return
+ *         Whether the error belongs to the given category.
+ */
+bool error_is_like(int error, int category);
+
+/**
+ * Equivalent to error_is_like(errno, category).
  */
-bool is_nonexistence_error(int error);
+bool errno_is_like(int category);
 
 #include <fcntl.h>
 
diff --git a/src/bftw.c b/src/bftw.c
index 355cb54..49f07df 100644
--- a/src/bftw.c
+++ b/src/bftw.c
@@ -68,7 +68,7 @@ const struct bfs_stat *bftw_stat(const struct BFTW *ftwbuf, enum bfs_stat_flags
 		}
 	} else {
 		ret = bftw_stat_impl(mutbuf, &mutbuf->stat_cache, BFS_STAT_FOLLOW);
-		if (!ret && (flags & BFS_STAT_TRYFOLLOW) && is_nonexistence_error(errno)) {
+		if (!ret && (flags & BFS_STAT_TRYFOLLOW) && errno_is_like(ENOENT)) {
 			ret = bftw_stat_impl(mutbuf, &mutbuf->lstat_cache, BFS_STAT_NOFOLLOW);
 		}
 	}
@@ -81,7 +81,7 @@ const struct bfs_stat *bftw_cached_stat(const struct BFTW *ftwbuf, enum bfs_stat
 		return ftwbuf->lstat_cache.buf;
 	} else if (ftwbuf->stat_cache.buf) {
 		return ftwbuf->stat_cache.buf;
-	} else if ((flags & BFS_STAT_TRYFOLLOW) && is_nonexistence_error(ftwbuf->stat_cache.error)) {
+	} else if ((flags & BFS_STAT_TRYFOLLOW) && error_is_like(ftwbuf->stat_cache.error, ENOENT)) {
 		return ftwbuf->lstat_cache.buf;
 	} else {
 		return NULL;
@@ -739,22 +739,10 @@ static int bftw_file_open(struct bftw_state *state, struct bftw_file *file, cons
 	}
 
 	int fd = bftw_file_openat(state, file, base, at_path);
-	if (fd >= 0) {
+	if (fd >= 0 || !errno_is_like(ENAMETOOLONG)) {
 		return fd;
 	}
 
-	switch (errno) {
-	case ENAMETOOLONG:
-#if __DragonFly__
-	// https://twitter.com/tavianator/status/1742991411203485713
-	case EFAULT:
-#endif
-		break;
-
-	default:
-		return -1;
-	}
-
 	// Handle ENAMETOOLONG by manually traversing the path component-by-component
 	struct bftw_list parents;
 	SLIST_INIT(&parents);
diff --git a/src/eval.c b/src/eval.c
index 130b366..1a814b3 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -80,7 +80,7 @@ static void eval_error(struct bfs_eval *state, const char *format, ...) {
  */
 static bool eval_should_ignore(const struct bfs_eval *state, int error) {
 	return state->ctx->ignore_races
-		&& is_nonexistence_error(error)
+		&& error_is_like(error, ENOENT)
 		&& state->ftwbuf->depth > 0;
 }
 
diff --git a/src/stat.c b/src/stat.c
index d7387c6..91aa092 100644
--- a/src/stat.c
+++ b/src/stat.c
@@ -260,7 +260,7 @@ static int bfs_stat_tryfollow(int at_fd, const char *at_path, int at_flags, int
 
 	if (ret != 0
 	    && (bfs_flags & (BFS_STAT_NOFOLLOW | BFS_STAT_TRYFOLLOW)) == BFS_STAT_TRYFOLLOW
-	    && is_nonexistence_error(errno))
+	    && errno_is_like(ENOENT))
 	{
 		at_flags |= AT_SYMLINK_NOFOLLOW;
 		ret = bfs_stat_explicit(at_fd, at_path, at_flags, x_flags, buf);
diff --git a/tests/xtouch.c b/tests/xtouch.c
index ed8bbee..6099128 100644
--- a/tests/xtouch.c
+++ b/tests/xtouch.c
@@ -68,22 +68,11 @@ static int open_parent(const struct args *args, const char **path) {
 		goto done;
 	}
 
-	switch (errno) {
-	case ENAMETOOLONG:
-#if __DragonFly__
-	// https://twitter.com/tavianator/status/1742991411203485713
-	case EFAULT:
-#endif
-		break;
-
-	case ENOENT:
-		if (args->flags & CREATE_PARENTS) {
-			break;
-		} else {
+	if (errno == ENOENT) {
+		if (!(args->flags & CREATE_PARENTS)) {
 			goto err;
 		}
-
-	default:
+	} else if (!errno_is_like(ENAMETOOLONG)) {
 		goto err;
 	}