From d78a95d751069bcf48395cfd08e455138712f247 Mon Sep 17 00:00:00 2001
From: Lennart Poettering <lennart@poettering.net>
Date: Thu, 9 Apr 2020 11:56:23 +0200
Subject: [PATCH] btrfs-util: define helper that creates a btrfs subvol if we
 can, and a directory as fallback

---
 src/basic/btrfs-util.c | 25 +++++++++++++++++++++++++
 src/basic/btrfs-util.h |  2 ++
 2 files changed, 27 insertions(+)

diff --git a/src/basic/btrfs-util.c b/src/basic/btrfs-util.c
index 18a72177579..68367dfbd6e 100644
--- a/src/basic/btrfs-util.c
+++ b/src/basic/btrfs-util.c
@@ -160,6 +160,31 @@ int btrfs_subvol_make(const char *path) {
         return btrfs_subvol_make_fd(fd, subvolume);
 }
 
+int btrfs_subvol_make_fallback(const char *path, mode_t mode) {
+        mode_t old, combined;
+        int r;
+
+        assert(path);
+
+        /* Let's work like mkdir(), i.e. take the specified mode, and mask it with the current umask. */
+        old = umask(~mode);
+        combined = old | ~mode;
+        if (combined != ~mode)
+                umask(combined);
+        r = btrfs_subvol_make(path);
+        umask(old);
+
+        if (r >= 0)
+                return 1; /* subvol worked */
+        if (r != -ENOTTY)
+                return r;
+
+        if (mkdir(path, mode) < 0)
+                return -errno;
+
+        return 0; /* plain directory */
+}
+
 int btrfs_subvol_set_read_only_fd(int fd, bool b) {
         uint64_t flags, nflags;
         struct stat st;
diff --git a/src/basic/btrfs-util.h b/src/basic/btrfs-util.h
index b15667bf2f8..c1bbb42ca1b 100644
--- a/src/basic/btrfs-util.h
+++ b/src/basic/btrfs-util.h
@@ -66,6 +66,8 @@ int btrfs_quota_scan_ongoing(int fd);
 int btrfs_subvol_make(const char *path);
 int btrfs_subvol_make_fd(int fd, const char *subvolume);
 
+int btrfs_subvol_make_fallback(const char *path, mode_t);
+
 int btrfs_subvol_snapshot_fd_full(int old_fd, const char *new_path, BtrfsSnapshotFlags flags, copy_progress_path_t progress_path, copy_progress_bytes_t progress_bytes, void *userdata);
 static inline int btrfs_subvol_snapshot_fd(int old_fd, const char *new_path, BtrfsSnapshotFlags flags) {
         return btrfs_subvol_snapshot_fd_full(old_fd, new_path, flags, NULL, NULL, NULL);