[PATCH 5/5] io_uring: add link opcode for current working directory

[Usama Arif <usama.arif@bytedance.com>]

This provides consistency between io_uring and the respective I/O syscall
and avoids having the user of liburing specify the cwd in sqe for
IORING_OP_LINKAT.

Signed-off-by: Usama Arif <usama.arif@bytedance.com>
---
 fs/io_uring.c                 | 29 ++++++++++++++++++++---------
 include/uapi/linux/io_uring.h |  1 +
 2 files changed, 21 insertions(+), 9 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 4050377619d3..31dfad3a7312 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1314,6 +1314,7 @@ static const struct io_op_def io_op_defs[] = {
 	[IORING_OP_MKDIRAT] = {},
 	[IORING_OP_SYMLINK] = {},
 	[IORING_OP_SYMLINKAT] = {},
+	[IORING_OP_LINK] = {},
 	[IORING_OP_LINKAT] = {},
 	[IORING_OP_MSG_RING] = {
 		.needs_file		= 1,
@@ -1469,6 +1470,8 @@ const char *io_uring_get_opcode(u8 opcode)
 		return "SYMLINK";
 	case IORING_OP_SYMLINKAT:
 		return "SYMLINKAT";
+	case IORING_OP_LINK:
+		return "LINK";
 	case IORING_OP_LINKAT:
 		return "LINKAT";
 	case IORING_OP_MSG_RING:
@@ -4991,8 +4994,8 @@ static int io_symlink(struct io_kiocb *req, unsigned int issue_flags)
 	return 0;
 }
 
-static int io_linkat_prep(struct io_kiocb *req,
-			    const struct io_uring_sqe *sqe)
+static int io_link_prep(struct io_kiocb *req,
+			    const struct io_uring_sqe *sqe, bool is_cwd)
 {
 	struct io_hardlink *lnk = &req->hardlink;
 	const char __user *oldf, *newf;
@@ -5002,8 +5005,12 @@ static int io_linkat_prep(struct io_kiocb *req,
 	if (unlikely(req->flags & REQ_F_FIXED_FILE))
 		return -EBADF;
 
-	lnk->old_dfd = READ_ONCE(sqe->fd);
-	lnk->new_dfd = READ_ONCE(sqe->len);
+	if (is_cwd) {
+		lnk->old_dfd = lnk->new_dfd = AT_FDCWD;
+	} else {
+		lnk->old_dfd = READ_ONCE(sqe->fd);
+		lnk->new_dfd = READ_ONCE(sqe->len);
+	}
 	oldf = u64_to_user_ptr(READ_ONCE(sqe->addr));
 	newf = u64_to_user_ptr(READ_ONCE(sqe->addr2));
 	lnk->flags = READ_ONCE(sqe->hardlink_flags);
@@ -5022,7 +5029,7 @@ static int io_linkat_prep(struct io_kiocb *req,
 	return 0;
 }
 
-static int io_linkat(struct io_kiocb *req, unsigned int issue_flags)
+static int io_link(struct io_kiocb *req, unsigned int issue_flags)
 {
 	struct io_hardlink *lnk = &req->hardlink;
 	int ret;
@@ -8117,8 +8124,10 @@ static int io_req_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 		return io_symlink_prep(req, sqe, 1);
 	case IORING_OP_SYMLINKAT:
 		return io_symlink_prep(req, sqe, 0);
+	case IORING_OP_LINK:
+		return io_link_prep(req, sqe, 1);
 	case IORING_OP_LINKAT:
-		return io_linkat_prep(req, sqe);
+		return io_link_prep(req, sqe, 0);
 	case IORING_OP_MSG_RING:
 		return io_msg_ring_prep(req, sqe);
 	case IORING_OP_FSETXATTR:
@@ -8280,6 +8289,7 @@ static void io_clean_op(struct io_kiocb *req)
 			putname(req->symlink.oldpath);
 			putname(req->symlink.newpath);
 			break;
+		case IORING_OP_LINK:
 		case IORING_OP_LINKAT:
 			putname(req->hardlink.oldpath);
 			putname(req->hardlink.newpath);
@@ -8442,14 +8452,15 @@ static int io_issue_sqe(struct io_kiocb *req, unsigned int issue_flags)
 		break;
 	case IORING_OP_MKDIR:
 	case IORING_OP_MKDIRAT:
-		ret = io_mkdirat(req, issue_flags);
+		ret = io_mkdir(req, issue_flags);
 		break;
 	case IORING_OP_SYMLINK:
 	case IORING_OP_SYMLINKAT:
-		ret = io_symlinkat(req, issue_flags);
+		ret = io_symlink(req, issue_flags);
 		break;
+	case IORING_OP_LINK:
 	case IORING_OP_LINKAT:
-		ret = io_linkat(req, issue_flags);
+		ret = io_link(req, issue_flags);
 		break;
 	case IORING_OP_MSG_RING:
 		ret = io_msg_ring(req, issue_flags);
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 74e6b70638ee..41391a762ad1 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -193,6 +193,7 @@ enum io_uring_op {
 	IORING_OP_UNLINK,
 	IORING_OP_MKDIR,
 	IORING_OP_SYMLINK,
+	IORING_OP_LINK,
 
 	/* this goes last, obviously */
 	IORING_OP_LAST,
-- 
2.25.1