Add get_path()

Implement a fallback mechanism for opening paths to a filesystem. If
explicitly given, use that. If env var is set, use that. Otherwise, use
current working directory.

Use wordexp to expand ~, $HOME, etc.

Signed-off-by: Andy Grover <agrover@versity.com>

utils/src/dev.h

@@ -1,7 +1,7 @@
 #ifndef _DEV_H_
 #define _DEV_H_
 
-#define BASE_SIZE_FMT "%.2f %s"
+#define BASE_SIZE_FMT "%.2f%s"
 #define BASE_SIZE_ARGS(sz) size_flt(sz, 1), size_str(sz, 1)
 
 #define SIZE_FMT "%llu (%.2f %s)"

utils/src/util.c

@@ -0,0 +1,70 @@
+#define _GNU_SOURCE
+#include <unistd.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <string.h>
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <wordexp.h>
+
+#include "util.h"
+
+static int open_path(char *path, int flags)
+{
+	wordexp_t exp_result;
+	int ret;
+
+	ret = wordexp(path, &exp_result, WRDE_NOCMD | WRDE_SHOWERR | WRDE_UNDEF);
+	if (ret) {
+		fprintf(stderr, "wordexp() failure for \"%s\": %d\n", path, ret);
+		ret = -EINVAL;
+		goto out;
+	}
+
+	ret = open(exp_result.we_wordv[0], flags);
+	if (ret < 0) {
+		ret = -errno;
+		fprintf(stderr, "failed to open '%s': %s (%d)\n",
+			path, strerror(errno), errno);
+	}
+
+out:
+	wordfree(&exp_result);
+
+	return ret;
+}
+
+/*
+ * 1. if path option given, use that
+ * 2. if env var, use that
+ * 3. if cwd is in a scoutfs fs, use that
+ * 4. else error
+ */
+int get_path(char *path, int flags)
+{
+	char *env_path;
+	char *cur_dir_path;
+	int ret;
+
+	if (path)
+		return open_path(path, flags);
+
+	env_path = getenv("SCOUTFS_PATH");
+	if (env_path)
+		return open_path(path, flags);
+
+	cur_dir_path = get_current_dir_name();
+	if (!cur_dir_path) {
+		ret = -errno;
+		return ret;
+	}
+
+	ret = open_path(cur_dir_path, flags);
+	free(cur_dir_path);
+
+	// TODO: check this is within a scoutfs mount?
+
+	return ret;
+}

utils/src/util.h

@@ -111,4 +111,6 @@ static inline int memcmp_lens(const void *a, int a_len,
 	return memcmp(a, b, len) ?: a_len - b_len;
 }
 
+int get_path(char *path, int flags);
+
 #endif