[PATCH v3 1/3] fs: dispatch null_dev_desc_ok filesystems before lookup

[Vincent Jardin]

Filesystems that are null_dev_desc_ok (semihosting, ubifs) have
no UCLASS_BLK device under their ifname, so on real hardware
fs_set_blk_dev() always fails at the partition lookup.
The workaround was to add a per-filesystem
command (example cmd/ubifs.c), which duplicates the plumbing of
fstype_info.

Probe such entries with block_desc=NULL up front, so
  load semihosting <addr> <file>
works without a new command.

Sandbox boards that exercise the existing fallback through "host
bind" stay unchanged.

Signed-off-by: Vincent Jardin <vjardin at free.fr>

---

Changes in v3:
- Apply Simon Glass's v1 review:
    * Fix typo "thue" -> "the" in the commit body
    * Refactor the dispatch loop with a fs_lookup_null_dev_info()
      helper
- Add doc/usage/cmd/load.rst "Null-block-device interfaces"
- Add pytest regression tests for the `semihosting` and
  sandbox ifnames, verified passing on qemu_arm64 (with
  CONFIG_SEMIHOSTING=y) and on a sandbox build respectively. A
  ubifs test is intentionally not done.

Changes in v2:
- (v2 is my local iteration, not good for the list; the changes
  since v1 are captured in the v3 changelog below.)

 fs/fs.c | 42 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/fs/fs.c b/fs/fs.c
index 8ea50a6c13c..56f3e0c9204 100644
--- a/fs/fs.c
+++ b/fs/fs.c
@@ -459,11 +459,53 @@ const char *fs_get_type_name(void)
 	return fs_get_info(fs_type)->name;
 }
 
+/*
+ * Some fstypes (semihosting, ubifs) have no underlying block device
+ * and ignore the block_desc argument of their probe hook. The legacy
+ * commands (ubifsload, semihosting via env macros) just pass NULL;
+ * for "load <iface> ..." to behave the same, the dispatcher opts
+ * those fstypes in by name here, before any block-device lookup is
+ * attempted.
+ *
+ * Returns the matching fstype_info if @ifname names a fstype that
+ * opts into null_dev_desc_ok dispatch and the caller's @fstype filter
+ * permits it. Returns NULL otherwise.
+ */
+static struct fstype_info *fs_lookup_null_dev_info(const char *ifname,
+						   int fstype)
+{
+	struct fstype_info *info;
+	int i;
+
+	for (i = 0, info = fstypes; i < ARRAY_SIZE(fstypes); i++, info++) {
+		if (fstype != FS_TYPE_ANY && info->fstype != FS_TYPE_ANY &&
+		    fstype != info->fstype)
+			continue;
+		if (!info->null_dev_desc_ok || !info->name)
+			continue;
+		if (!strcmp(info->name, ifname))
+			return info;
+	}
+
+	return NULL;
+}
+
 int fs_set_blk_dev(const char *ifname, const char *dev_part_str, int fstype)
 {
 	struct fstype_info *info;
 	int part, i;
 
+	info = fs_lookup_null_dev_info(ifname, fstype);
+	if (info) {
+		fs_dev_desc = NULL;
+		memset(&fs_partition, 0, sizeof(fs_partition));
+		if (!info->probe(NULL, &fs_partition)) {
+			fs_type = info->fstype;
+			fs_dev_part = 0;
+			return 0;
+		}
+	}
+
 	part = part_get_info_by_dev_and_name_or_num(ifname, dev_part_str, &fs_dev_desc,
 						    &fs_partition, 1);
 	if (part < 0)
-- 
2.43.0