fs: jbd2: Add jbd2_journal_init_global() for ext4l

Add jbd2_journal_init_global() which initializes the JBD2 journal
subsystem caches. This wraps the existing journal_init() with a
static guard to ensure it's only called once.

Call this from ext4l_probe() when CONFIG_EXT4_JOURNAL is enabled
to initialize the journal subsystem before any journal operations.

Co-developed-by: Claude Opus 4.5 <noreply@anthropic.com>
Signed-off-by: Simon Glass <simon.glass@canonical.com>

fs/ext4l/interface.c

@@ -13,6 +13,7 @@
 #include <malloc.h>
 #include <asm/byteorder.h>
 #include <linux/errno.h>
+#include <linux/jbd2.h>
 #include <linux/types.h>
 
 #include "ext4_uboot.h"
@@ -33,6 +34,13 @@ int ext4l_probe(struct blk_desc *fs_dev_desc,
 	if (!fs_dev_desc)
 		return -EINVAL;
 
+	/* Initialise journal subsystem if enabled */
+	if (IS_ENABLED(CONFIG_EXT4_JOURNAL)) {
+		ret = jbd2_journal_init_global();
+		if (ret)
+			return ret;
+	}
+
 	buf = malloc(BLOCK_SIZE + 512);
 	if (!buf)
 		return -ENOMEM;

fs/jbd2/journal.c

@@ -3118,6 +3118,28 @@ static int __init journal_init(void)
 	return ret;
 }
 
+/**
+ * jbd2_journal_init_global() - Initialize JBD2 global state
+ *
+ * This must be called before any journal operations. It initializes
+ * the journal caches and other global state.
+ *
+ * Return: 0 on success, negative error code on failure
+ */
+int jbd2_journal_init_global(void)
+{
+	static bool initialized;
+
+	if (initialized)
+		return 0;
+
+	if (journal_init())
+		return -ENOMEM;
+
+	initialized = true;
+	return 0;
+}
+
 static void __exit journal_exit(void)
 {
 #ifdef CONFIG_JBD2_DEBUG