btrfs: send: add unlikely to all unexpected overflow checks

There are several checks for unexpected overflows of buffers and path
lengths that makes us fail the send operation with an error if for some
highly unexpected reason they happen. So add the unlikely tag to those
checks to hint the compiler to generate better code, while also making
it more explicit in the source that it's highly unexpected.

With gcc 14.2.0-19 from Debian on x86_64, I also got a small reduction
the text size of the btrfs module.

Before:

  $ size fs/btrfs/btrfs.ko
     text	   data	    bss	    dec	    hex	filename
  1936917	 162723	  15592	2115232	 2046a0	fs/btrfs/btrfs.ko

After:

  $ size fs/btrfs/btrfs.ko
     text	   data	    bss	    dec	    hex	filename
  1936789	 162723	  15592	2115104	 204620	fs/btrfs/btrfs.ko

Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

Author: fdmanana

fs/btrfs/send.c

@@ -1134,20 +1134,20 @@ static int iterate_dir_item(struct btrfs_root *root, struct btrfs_path *path,
 		btrfs_dir_item_key_to_cpu(eb, di, &di_key);
 
 		if (btrfs_dir_ftype(eb, di) == BTRFS_FT_XATTR) {
-			if (name_len > XATTR_NAME_MAX) {
+			if (unlikely(name_len > XATTR_NAME_MAX)) {
 				ret = -ENAMETOOLONG;
 				goto out;
 			}
-			if (name_len + data_len >
-					BTRFS_MAX_XATTR_SIZE(root->fs_info)) {
+			if (unlikely(name_len + data_len >
+				     BTRFS_MAX_XATTR_SIZE(root->fs_info))) {
 				ret = -E2BIG;
 				goto out;
 			}
 		} else {
 			/*
 			 * Path too long
 			 */
-			if (name_len + data_len > PATH_MAX) {
+			if (unlikely(name_len + data_len > PATH_MAX)) {
 				ret = -ENAMETOOLONG;
 				goto out;
 			}
@@ -5129,7 +5129,7 @@ static int process_verity(struct send_ctx *sctx)
 	if (ret < 0)
 		goto iput;
 
-	if (ret > FS_VERITY_MAX_DESCRIPTOR_SIZE) {
+	if (unlikely(ret > FS_VERITY_MAX_DESCRIPTOR_SIZE)) {
 		ret = -EMSGSIZE;
 		goto iput;
 	}
@@ -5173,14 +5173,14 @@ static int put_data_header(struct send_ctx *sctx, u32 len)
 		 * Since v2, the data attribute header doesn't include a length,
 		 * it is implicitly to the end of the command.
 		 */
-		if (sctx->send_max_size - sctx->send_size < sizeof(__le16) + len)
+		if (unlikely(sctx->send_max_size - sctx->send_size < sizeof(__le16) + len))
 			return -EOVERFLOW;
 		put_unaligned_le16(BTRFS_SEND_A_DATA, sctx->send_buf + sctx->send_size);
 		sctx->send_size += sizeof(__le16);
 	} else {
 		struct btrfs_tlv_header *hdr;
 
-		if (sctx->send_max_size - sctx->send_size < sizeof(*hdr) + len)
+		if (unlikely(sctx->send_max_size - sctx->send_size < sizeof(*hdr) + len))
 			return -EOVERFLOW;
 		hdr = (struct btrfs_tlv_header *)(sctx->send_buf + sctx->send_size);
 		put_unaligned_le16(BTRFS_SEND_A_DATA, &hdr->tlv_type);
@@ -5580,8 +5580,8 @@ static int send_encoded_extent(struct send_ctx *sctx, struct btrfs_path *path,
 	 * between the beginning of the command and the file data.
 	 */
 	data_offset = PAGE_ALIGN(sctx->send_size);
-	if (data_offset > sctx->send_max_size ||
-	    sctx->send_max_size - data_offset < disk_num_bytes) {
+	if (unlikely(data_offset > sctx->send_max_size ||
+		     sctx->send_max_size - data_offset < disk_num_bytes)) {
 		ret = -EOVERFLOW;
 		goto out;
 	}