io_uring/rsrc: change ubuf->ubuf_end to length tracking

If we change it to tracking ubuf->start + ubuf->len, then we can reduce
the size of struct io_mapped_ubuf by another 4 bytes, effectively 8
bytes, as a hole is eliminated too.

This shrinks io_mapped_ubuf to 32 bytes.
Signed-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/fdinfo.c

@@ -177,9 +177,8 @@ __cold void io_uring_show_fdinfo(struct seq_file *m, struct file *file)
 	seq_printf(m, "UserBufs:\t%u\n", ctx->nr_user_bufs);
 	for (i = 0; has_lock && i < ctx->nr_user_bufs; i++) {
 		struct io_mapped_ubuf *buf = ctx->user_bufs[i];
-		unsigned int len = buf->ubuf_end - buf->ubuf;
 
-		seq_printf(m, "%5u: 0x%llx/%u\n", i, buf->ubuf, len);
+		seq_printf(m, "%5u: 0x%llx/%u\n", i, buf->ubuf, buf->len);
 	}
 	if (has_lock && !xa_empty(&ctx->personalities)) {
 		unsigned long index;

io_uring/rsrc.c

@@ -38,7 +38,7 @@ static int io_sqe_buffer_register(struct io_ring_ctx *ctx, struct iovec *iov,
 static const struct io_mapped_ubuf dummy_ubuf = {
 	/* set invalid range, so io_import_fixed() fails meeting it */
 	.ubuf = -1UL,
-	.ubuf_end = 0,
+	.len = UINT_MAX,
 };
 
 int __io_account_mem(struct user_struct *user, unsigned long nr_pages)
@@ -985,7 +985,7 @@ static int io_sqe_buffer_register(struct io_ring_ctx *ctx, struct iovec *iov,
 	size = iov->iov_len;
 	/* store original address for later verification */
 	imu->ubuf = (unsigned long) iov->iov_base;
-	imu->ubuf_end = imu->ubuf + iov->iov_len;
+	imu->len = iov->iov_len;
 	imu->nr_bvecs = nr_pages;
 	imu->folio_shift = PAGE_SHIFT;
 	if (coalesced)
@@ -1086,7 +1086,7 @@ int io_import_fixed(int ddir, struct iov_iter *iter,
 	if (unlikely(check_add_overflow(buf_addr, (u64)len, &buf_end)))
 		return -EFAULT;
 	/* not inside the mapped region */
-	if (unlikely(buf_addr < imu->ubuf || buf_end > imu->ubuf_end))
+	if (unlikely(buf_addr < imu->ubuf || buf_end > (imu->ubuf + imu->len)))
 		return -EFAULT;
 
 	/*

io_uring/rsrc.h

@@ -42,11 +42,11 @@ struct io_rsrc_node {
 
 struct io_mapped_ubuf {
 	u64		ubuf;
-	u64		ubuf_end;
+	unsigned int	len;
 	unsigned int	nr_bvecs;
 	unsigned int    folio_shift;
-	unsigned long	acct_pages;
 	refcount_t	refs;
+	unsigned long	acct_pages;
 	struct bio_vec	bvec[] __counted_by(nr_bvecs);
 };