ext4l: Add page-io.c to build

Add the page I/O module (page-io.c) to the build. This implements
ext4's asynchronous page writeback infrastructure.

Stubs added for:
- bio structure and related operations
- folio_iter for bio iteration
- refcount operations (mapped to atomic)
- fscrypt bounce folio operations
- folio writeback operations
- writeback control operations
- i_write_hint member to inode struct

Remove stub functions now implemented in page-io.c:
- ext4_io_submit_init, ext4_init_io_end
- ext4_io_submit, ext4_put_io_end_defer
- ext4_put_io_end, ext4_alloc_io_end_vec

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

fs/ext4l/Makefile

@@ -8,6 +8,6 @@ obj-y := interface.o stub.o
 obj-y	+= balloc.o bitmap.o block_validity.o dir.o ext4_jbd2.o extents.o \
 		extents_status.o file.o fsync.o hash.o ialloc.o \
 		indirect.o inline.o inode.o mballoc.o \
-		namei.o super.o symlink.o xattr.o \
+		namei.o page_io.o super.o symlink.o xattr.o \
 		xattr_hurd.o xattr_trusted.o \
 		xattr_user.o orphan.o

fs/ext4l/ext4_uboot.h

@@ -834,6 +834,7 @@ struct inode {
 	atomic_t i_writecount;		/* Count of writers */
 	struct rw_semaphore i_rwsem;	/* inode lock */
 	const char *i_link;		/* Symlink target for fast symlinks */
+	unsigned short i_write_hint;	/* Write life time hint */
 };
 
 /* Inode time accessors */
@@ -1515,6 +1516,7 @@ static inline char *d_path(const struct path *path, char *buf, int buflen)
 /* fscrypt stubs - additional */
 #define fscrypt_inode_uses_fs_layer_crypto(i)	(0)
 #define fscrypt_decrypt_pagecache_blocks(f, l, o) ({ (void)(f); (void)(l); (void)(o); 0; })
+#define fscrypt_encrypt_pagecache_blocks(f, l, o, g) ({ (void)(f); (void)(l); (void)(o); (void)(g); (struct page *)NULL; })
 #define fscrypt_zeroout_range(i, lb, pb, l)	({ (void)(i); (void)(lb); (void)(pb); (void)(l); 0; })
 #define fscrypt_limit_io_blocks(i, lb, l)	(l)
 #define fscrypt_prepare_setattr(d, a)		({ (void)(d); (void)(a); 0; })
@@ -2565,4 +2567,101 @@ struct seq_operations {
 #define bdev_discard_granularity(bdev) \
 	({ (void)(bdev); 0U; })
 
+/*
+ * Stubs for page-io.c
+ */
+
+/* bio_vec - segment in a bio */
+struct bio_vec {
+	struct page *bv_page;
+	unsigned int bv_len;
+	unsigned int bv_offset;
+};
+
+/* bvec_iter - iterator for bio_vec */
+struct bvec_iter {
+	sector_t bi_sector;
+	unsigned int bi_size;
+	unsigned int bi_idx;
+	unsigned int bi_bvec_done;
+};
+
+/* bio - block I/O structure */
+struct bio {
+	struct bio *bi_next;
+	struct block_device *bi_bdev;
+	unsigned long bi_opf;
+	unsigned short bi_flags;
+	unsigned short bi_ioprio;
+	unsigned short bi_write_hint;
+	int bi_status;
+	struct bvec_iter bi_iter;
+	atomic_t __bi_remaining;
+	void *bi_private;
+	void (*bi_end_io)(struct bio *);
+};
+
+/* folio_iter for bio iteration */
+struct folio_iter {
+	int i;
+	struct folio *folio;
+	size_t offset;
+	size_t length;
+};
+
+/* bio operations - stubs */
+#define bio_for_each_folio_all(fi, bio) \
+	for ((fi).i = 0; (fi).i < 0; (fi).i++)
+#define bio_put(bio)			free(bio)
+#define bio_alloc(bdev, vecs, op, gfp)	((struct bio *)calloc(1, sizeof(struct bio)))
+#define submit_bio(bio)			do { } while (0)
+#define BIO_MAX_VECS			256
+
+/* refcount operations - map to atomic */
+#define refcount_set(r, v)		atomic_set((atomic_t *)(r), v)
+#define refcount_dec_and_test(r)	atomic_dec_and_test((atomic_t *)(r))
+#define refcount_inc(r)			atomic_inc((atomic_t *)(r))
+
+/* xchg - exchange value atomically */
+#define xchg(ptr, new)			({ typeof(*(ptr)) __old = *(ptr); *(ptr) = (new); __old; })
+
+/* printk_ratelimited - just use regular printk */
+#define printk_ratelimited(fmt, ...)	do { } while (0)
+
+/* mapping_set_error - record error in address_space */
+#define mapping_set_error(m, e)		do { (void)(m); (void)(e); } while (0)
+
+/* blk_status_to_errno - convert block status to errno */
+#define blk_status_to_errno(status)	(-(status))
+
+/* atomic_inc - increment atomic */
+#define atomic_inc(v)			((v)->counter++)
+
+/* GFP_NOIO - allocation without I/O */
+#define GFP_NOIO			0
+
+/* fscrypt stubs for page-io.c */
+#define fscrypt_is_bounce_folio(f)	({ (void)(f); 0; })
+#define fscrypt_pagecache_folio(f)	(f)
+#define fscrypt_free_bounce_page(p)	do { (void)(p); } while (0)
+#define fscrypt_set_bio_crypt_ctx_bh(bio, bh, gfp) \
+	do { (void)(bio); (void)(bh); (void)(gfp); } while (0)
+#define fscrypt_mergeable_bio_bh(bio, bh) \
+	({ (void)(bio); (void)(bh); 1; })
+
+/* folio writeback operations */
+#define folio_end_writeback(f)		do { (void)(f); } while (0)
+#define folio_start_writeback(f)	do { (void)(f); } while (0)
+#define folio_start_writeback_keepwrite(f) do { (void)(f); } while (0)
+bool __folio_start_writeback(struct folio *folio, bool keep_write);
+
+/* writeback control stubs */
+#define wbc_init_bio(wbc, bio)		do { (void)(wbc); (void)(bio); } while (0)
+#define wbc_account_cgroup_owner(wbc, folio, bytes) \
+	do { (void)(wbc); (void)(folio); (void)(bytes); } while (0)
+
+/* bio operations */
+#define bio_add_folio(bio, folio, len, off) \
+	({ (void)(bio); (void)(folio); (void)(len); (void)(off); 1; })
+
 #endif /* __EXT4_UBOOT_H__ */

fs/ext4l/page-io.c

@@ -7,24 +7,11 @@
  * Written by Theodore Ts'o, 2010.
  */
 
-#include <linux/fs.h>
+#include "ext4_uboot.h"
 #include <linux/time.h>
-#include <linux/highuid.h>
-#include <linux/pagemap.h>
-#include <linux/quotaops.h>
 #include <linux/string.h>
-#include <linux/buffer_head.h>
-#include <linux/writeback.h>
-#include <linux/pagevec.h>
 #include <linux/mpage.h>
-#include <linux/namei.h>
-#include <linux/uio.h>
-#include <linux/bio.h>
-#include <linux/workqueue.h>
 #include <linux/kernel.h>
-#include <linux/slab.h>
-#include <linux/mm.h>
-#include <linux/sched/mm.h>
 
 #include "ext4_jbd2.h"
 #include "xattr.h"

fs/ext4l/stub.c

@@ -199,6 +199,14 @@ int ext4_fc_replay_check_excluded(struct super_block *sb, unsigned long long blk
 	return 0;
 }
 
+/*
+ * Stubs for page-io.c
+ */
+bool __folio_start_writeback(struct folio *folio, bool keep_write)
+{
+	return false;
+}
+
 /* ext4_read_bh is now in super.c */
 /* ext4_sb_bread_nofail is now in super.c */
 
@@ -262,34 +270,7 @@ int ext4_fc_commit(void *journal, unsigned int tid)
 
 /* Inline data is now in inline.c */
 
-/* I/O submit */
-void ext4_io_submit_init(void *io, void *wbc)
-{
-}
-
-
-void *ext4_init_io_end(struct inode *inode, int gfp)
-{
-	return NULL;
-}
-
-void ext4_io_submit(void *io)
-{
-}
-
-void ext4_put_io_end_defer(void *io_end)
-{
-}
-
-void ext4_put_io_end(void *io_end)
-{
-}
-
-void *ext4_alloc_io_end_vec(void *io_end, unsigned long num)
-{
-	return NULL;
-}
-
+/* I/O submit stubs are now in page-io.c */
 
 /* JBD2 ordered truncate */
 int jbd2_journal_begin_ordered_truncate(void *ji, loff_t new_size)