[PATCH v7 00/10] io_uring: add mkdir and [sym]linkat support

[PATCH v7 00/10] io_uring: add mkdir and [sym]linkat support

[Dmitry Kadashev]

This started out as an attempt to add mkdirat support to io_uring which
is heavily based on renameat() / unlinkat() support.

During the review process more operations were added (linkat, symlinkat,
mknodat) mainly to keep things uniform internally (in namei.c), and
with things changed in namei.c adding support for these operations to
io_uring is trivial, so that was done too (except for mknodat). See
https://lore.kernel.org/io-uring/20210514145259.wtl4xcsp52woi6ab@wittgenstein/

The first patch makes putname() ignore IS_ERR_OR_NULL names and converts
a couple of places where the check was already implemented in the
callers. No functional changes.

The second patch is preparation with no functional changes, makes
do_mkdirat accept struct filename pointer rather than the user string.

The third one leverages that to implement mkdirat in io_uring.

4-7 just convert other similar do_* functions in namei.c to accept
struct filename, for uniformity with do_mkdirat, do_renameat and
do_unlinkat. No functional changes there.

8 changes do_* helpers in namei.c to return ints rather than some of
them returning ints and some longs.

9-10 add symlinkat and linkat support to io_uring correspondingly.

Based on for-5.14/io_uring.

v7:
- rebase
- make putname() ignore IS_ERR_OR_NULL names, remove conditional calls
  to it from the callers

v6:

- rebase
- add safety checks for IOPOLL mode
- add safety checks for unused sqe parts
- drop mknodat support from io_uring as requested by Jens
- add Christian's Acked-by

v5:
- rebase
- add symlinkat, linkat and mknodat support to io_uring

v4:
- update do_mknodat, do_symlinkat and do_linkat to accept struct
  filename for uniformity with do_mkdirat, do_renameat and do_unlinkat;

v3:
- rebase;

v2:
- do not mess with struct filename's refcount in do_mkdirat, instead add
  and use __filename_create() that does not drop the name on success;

Dmitry Kadashev (10):
  namei: ignore ERR/NULL names in putname()
  fs: make do_mkdirat() take struct filename
  io_uring: add support for IORING_OP_MKDIRAT
  fs: make do_mknodat() take struct filename
  fs: make do_symlinkat() take struct filename
  namei: add getname_uflags()
  fs: make do_linkat() take struct filename
  fs: update do_*() helpers to return ints
  io_uring: add support for IORING_OP_SYMLINKAT
  io_uring: add support for IORING_OP_LINKAT

 fs/exec.c                     |   8 +-
 fs/internal.h                 |   8 +-
 fs/io_uring.c                 | 196 ++++++++++++++++++++++++++++++++++
 fs/namei.c                    | 139 +++++++++++++++---------
 include/linux/fs.h            |   1 +
 include/uapi/linux/io_uring.h |   4 +
 6 files changed, 300 insertions(+), 56 deletions(-)

-- 
2.30.2

[PATCH v7 01/10] namei: ignore ERR/NULL names in putname()

[Dmitry Kadashev]

Supporting ERR/NULL names in putname() makes callers code cleaner, and
is what some other path walking functions already support for the same
reason.

This also removes a few existing IS_ERR checks before putname().

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/io-uring/CAHk-=wgCac9hBsYzKMpHk0EbLgQaXR=OUAjHaBtaY+G8A9KhFg@mail.gmail.com/
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Dmitry Kadashev <dkadashev@gmail.com>
---
 fs/namei.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 79b0ff9b151e..70caf4ef1134 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -247,6 +247,9 @@ getname_kernel(const char * filename)
 
 void putname(struct filename *name)
 {
+	if (IS_ERR_OR_NULL(name))
+		return;
+
 	BUG_ON(name->refcnt <= 0);
 
 	if (--name->refcnt > 0)
@@ -4718,11 +4721,9 @@ int do_renameat2(int olddfd, struct filename *from, int newdfd,
 		goto retry;
 	}
 put_both:
-	if (!IS_ERR(from))
-		putname(from);
+	putname(from);
 put_new:
-	if (!IS_ERR(to))
-		putname(to);
+	putname(to);
 	return error;
 }
 
-- 
2.30.2

[PATCH v7 02/10] fs: make do_mkdirat() take struct filename

[Dmitry Kadashev]

Pass in the struct filename pointers instead of the user string, and
update the three callers to do the same. This is heavily based on
commit dbea8d345177 ("fs: make do_renameat2() take struct filename").

This behaves like do_unlinkat() and do_renameat2().

Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Dmitry Kadashev <dkadashev@gmail.com>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
---
 fs/internal.h |  1 +
 fs/namei.c    | 22 ++++++++++++++++------
 2 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/fs/internal.h b/fs/internal.h
index 6aeae7ef3380..848e165ef0f1 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -77,6 +77,7 @@ long do_unlinkat(int dfd, struct filename *name);
 int may_linkat(struct user_namespace *mnt_userns, struct path *link);
 int do_renameat2(int olddfd, struct filename *oldname, int newdfd,
 		 struct filename *newname, unsigned int flags);
+long do_mkdirat(int dfd, struct filename *name, umode_t mode);
 
 /*
  * namespace.c
diff --git a/fs/namei.c b/fs/namei.c
index 70caf4ef1134..8bc65fd357ad 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -3559,7 +3559,7 @@ struct file *do_file_open_root(struct dentry *dentry, struct vfsmount *mnt,
 	return file;
 }
 
-static struct dentry *filename_create(int dfd, struct filename *name,
+static struct dentry *__filename_create(int dfd, struct filename *name,
 				struct path *path, unsigned int lookup_flags)
 {
 	struct dentry *dentry = ERR_PTR(-EEXIST);
@@ -3615,7 +3615,6 @@ static struct dentry *filename_create(int dfd, struct filename *name,
 		error = err2;
 		goto fail;
 	}
-	putname(name);
 	return dentry;
 fail:
 	dput(dentry);
@@ -3630,6 +3629,16 @@ static struct dentry *filename_create(int dfd, struct filename *name,
 	return dentry;
 }
 
+static inline struct dentry *filename_create(int dfd, struct filename *name,
+				struct path *path, unsigned int lookup_flags)
+{
+	struct dentry *res = __filename_create(dfd, name, path, lookup_flags);
+
+	if (!IS_ERR(res))
+		putname(name);
+	return res;
+}
+
 struct dentry *kern_path_create(int dfd, const char *pathname,
 				struct path *path, unsigned int lookup_flags)
 {
@@ -3820,7 +3829,7 @@ int vfs_mkdir(struct user_namespace *mnt_userns, struct inode *dir,
 }
 EXPORT_SYMBOL(vfs_mkdir);
 
-static long do_mkdirat(int dfd, const char __user *pathname, umode_t mode)
+long do_mkdirat(int dfd, struct filename *name, umode_t mode)
 {
 	struct dentry *dentry;
 	struct path path;
@@ -3828,7 +3837,7 @@ static long do_mkdirat(int dfd, const char __user *pathname, umode_t mode)
 	unsigned int lookup_flags = LOOKUP_DIRECTORY;
 
 retry:
-	dentry = user_path_create(dfd, pathname, &path, lookup_flags);
+	dentry = __filename_create(dfd, name, &path, lookup_flags);
 	if (IS_ERR(dentry))
 		return PTR_ERR(dentry);
 
@@ -3846,17 +3855,18 @@ static long do_mkdirat(int dfd, const char __user *pathname, umode_t mode)
 		lookup_flags |= LOOKUP_REVAL;
 		goto retry;
 	}
+	putname(name);
 	return error;
 }
 
 SYSCALL_DEFINE3(mkdirat, int, dfd, const char __user *, pathname, umode_t, mode)
 {
-	return do_mkdirat(dfd, pathname, mode);
+	return do_mkdirat(dfd, getname(pathname), mode);
 }
 
 SYSCALL_DEFINE2(mkdir, const char __user *, pathname, umode_t, mode)
 {
-	return do_mkdirat(AT_FDCWD, pathname, mode);
+	return do_mkdirat(AT_FDCWD, getname(pathname), mode);
 }
 
 /**
-- 
2.30.2

[PATCH v7 03/10] io_uring: add support for IORING_OP_MKDIRAT

[Dmitry Kadashev]

IORING_OP_MKDIRAT behaves like mkdirat(2) and takes the same flags
and arguments.

Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Dmitry Kadashev <dkadashev@gmail.com>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
---
 fs/io_uring.c                 | 59 +++++++++++++++++++++++++++++++++++
 include/uapi/linux/io_uring.h |  1 +
 2 files changed, 60 insertions(+)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 5b840bb1e8ec..42d54f9bbbb2 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -674,6 +674,13 @@ struct io_unlink {
 	struct filename			*filename;
 };
 
+struct io_mkdir {
+	struct file			*file;
+	int				dfd;
+	umode_t				mode;
+	struct filename			*filename;
+};
+
 struct io_completion {
 	struct file			*file;
 	struct list_head		list;
@@ -831,6 +838,7 @@ struct io_kiocb {
 		struct io_shutdown	shutdown;
 		struct io_rename	rename;
 		struct io_unlink	unlink;
+		struct io_mkdir		mkdir;
 		/* use only after cleaning per-op data, see io_clean_op() */
 		struct io_completion	compl;
 	};
@@ -1042,6 +1050,7 @@ static const struct io_op_def io_op_defs[] = {
 	},
 	[IORING_OP_RENAMEAT] = {},
 	[IORING_OP_UNLINKAT] = {},
+	[IORING_OP_MKDIRAT] = {},
 };
 
 static bool io_disarm_next(struct io_kiocb *req);
@@ -3545,6 +3554,48 @@ static int io_unlinkat(struct io_kiocb *req, unsigned int issue_flags)
 	return 0;
 }
 
+static int io_mkdirat_prep(struct io_kiocb *req,
+			    const struct io_uring_sqe *sqe)
+{
+	struct io_mkdir *mkd = &req->mkdir;
+	const char __user *fname;
+
+	if (unlikely(req->ctx->flags & IORING_SETUP_IOPOLL))
+		return -EINVAL;
+	if (sqe->ioprio || sqe->off || sqe->rw_flags || sqe->buf_index)
+		return -EINVAL;
+	if (unlikely(req->flags & REQ_F_FIXED_FILE))
+		return -EBADF;
+
+	mkd->dfd = READ_ONCE(sqe->fd);
+	mkd->mode = READ_ONCE(sqe->len);
+
+	fname = u64_to_user_ptr(READ_ONCE(sqe->addr));
+	mkd->filename = getname(fname);
+	if (IS_ERR(mkd->filename))
+		return PTR_ERR(mkd->filename);
+
+	req->flags |= REQ_F_NEED_CLEANUP;
+	return 0;
+}
+
+static int io_mkdirat(struct io_kiocb *req, int issue_flags)
+{
+	struct io_mkdir *mkd = &req->mkdir;
+	int ret;
+
+	if (issue_flags & IO_URING_F_NONBLOCK)
+		return -EAGAIN;
+
+	ret = do_mkdirat(mkd->dfd, mkd->filename, mkd->mode);
+
+	req->flags &= ~REQ_F_NEED_CLEANUP;
+	if (ret < 0)
+		req_set_fail(req);
+	io_req_complete(req, ret);
+	return 0;
+}
+
 static int io_shutdown_prep(struct io_kiocb *req,
 			    const struct io_uring_sqe *sqe)
 {
@@ -5953,6 +6004,8 @@ static int io_req_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 		return io_renameat_prep(req, sqe);
 	case IORING_OP_UNLINKAT:
 		return io_unlinkat_prep(req, sqe);
+	case IORING_OP_MKDIRAT:
+		return io_mkdirat_prep(req, sqe);
 	}
 
 	printk_once(KERN_WARNING "io_uring: unhandled opcode %d\n",
@@ -6114,6 +6167,9 @@ static void io_clean_op(struct io_kiocb *req)
 		case IORING_OP_UNLINKAT:
 			putname(req->unlink.filename);
 			break;
+		case IORING_OP_MKDIRAT:
+			putname(req->mkdir.filename);
+			break;
 		}
 	}
 	if ((req->flags & REQ_F_POLLED) && req->apoll) {
@@ -6242,6 +6298,9 @@ static int io_issue_sqe(struct io_kiocb *req, unsigned int issue_flags)
 	case IORING_OP_UNLINKAT:
 		ret = io_unlinkat(req, issue_flags);
 		break;
+	case IORING_OP_MKDIRAT:
+		ret = io_mkdirat(req, issue_flags);
+		break;
 	default:
 		ret = -EINVAL;
 		break;
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 79126d5cd289..a926407c230e 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -133,6 +133,7 @@ enum {
 	IORING_OP_SHUTDOWN,
 	IORING_OP_RENAMEAT,
 	IORING_OP_UNLINKAT,
+	IORING_OP_MKDIRAT,
 
 	/* this goes last, obviously */
 	IORING_OP_LAST,
-- 
2.30.2

[PATCH v7 04/10] fs: make do_mknodat() take struct filename

[Dmitry Kadashev]

Pass in the struct filename pointers instead of the user string, for
uniformity with the recently converted do_unlinkat(), do_renameat(),
do_mkdirat().

Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <christian.brauner@ubuntu.com>
Link: https://lore.kernel.org/io-uring/20210330071700.kpjoyp5zlni7uejm@wittgenstein/
Signed-off-by: Dmitry Kadashev <dkadashev@gmail.com>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
---
 fs/namei.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 8bc65fd357ad..34b8968dec92 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -3727,7 +3727,7 @@ static int may_mknod(umode_t mode)
 	}
 }
 
-static long do_mknodat(int dfd, const char __user *filename, umode_t mode,
+static long do_mknodat(int dfd, struct filename *name, umode_t mode,
 		unsigned int dev)
 {
 	struct user_namespace *mnt_userns;
@@ -3738,9 +3738,9 @@ static long do_mknodat(int dfd, const char __user *filename, umode_t mode,
 
 	error = may_mknod(mode);
 	if (error)
-		return error;
+		goto out1;
 retry:
-	dentry = user_path_create(dfd, filename, &path, lookup_flags);
+	dentry = __filename_create(dfd, name, &path, lookup_flags);
 	if (IS_ERR(dentry))
 		return PTR_ERR(dentry);
 
@@ -3748,7 +3748,7 @@ static long do_mknodat(int dfd, const char __user *filename, umode_t mode,
 		mode &= ~current_umask();
 	error = security_path_mknod(&path, dentry, mode, dev);
 	if (error)
-		goto out;
+		goto out2;
 
 	mnt_userns = mnt_user_ns(path.mnt);
 	switch (mode & S_IFMT) {
@@ -3767,24 +3767,26 @@ static long do_mknodat(int dfd, const char __user *filename, umode_t mode,
 					  dentry, mode, 0);
 			break;
 	}
-out:
+out2:
 	done_path_create(&path, dentry);
 	if (retry_estale(error, lookup_flags)) {
 		lookup_flags |= LOOKUP_REVAL;
 		goto retry;
 	}
+out1:
+	putname(name);
 	return error;
 }
 
 SYSCALL_DEFINE4(mknodat, int, dfd, const char __user *, filename, umode_t, mode,
 		unsigned int, dev)
 {
-	return do_mknodat(dfd, filename, mode, dev);
+	return do_mknodat(dfd, getname(filename), mode, dev);
 }
 
 SYSCALL_DEFINE3(mknod, const char __user *, filename, umode_t, mode, unsigned, dev)
 {
-	return do_mknodat(AT_FDCWD, filename, mode, dev);
+	return do_mknodat(AT_FDCWD, getname(filename), mode, dev);
 }
 
 /**
-- 
2.30.2

[PATCH v7 05/10] fs: make do_symlinkat() take struct filename

[Dmitry Kadashev]

Pass in the struct filename pointers instead of the user string, for
uniformity with the recently converted do_mkdnodat(), do_unlinkat(),
do_renameat(), do_mkdirat().

Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <christian.brauner@ubuntu.com>
Link: https://lore.kernel.org/io-uring/20210330071700.kpjoyp5zlni7uejm@wittgenstein/
Signed-off-by: Dmitry Kadashev <dkadashev@gmail.com>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
---
 fs/namei.c | 24 +++++++++++++-----------
 1 file changed, 13 insertions(+), 11 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 34b8968dec92..57170d57e84d 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -4191,23 +4191,23 @@ int vfs_symlink(struct user_namespace *mnt_userns, struct inode *dir,
 }
 EXPORT_SYMBOL(vfs_symlink);
 
-static long do_symlinkat(const char __user *oldname, int newdfd,
-		  const char __user *newname)
+static long do_symlinkat(struct filename *from, int newdfd,
+		  struct filename *to)
 {
 	int error;
-	struct filename *from;
 	struct dentry *dentry;
 	struct path path;
 	unsigned int lookup_flags = 0;
 
-	from = getname(oldname);
-	if (IS_ERR(from))
-		return PTR_ERR(from);
+	if (IS_ERR(from)) {
+		error = PTR_ERR(from);
+		goto out_putboth;
+	}
 retry:
-	dentry = user_path_create(newdfd, newname, &path, lookup_flags);
+	dentry = __filename_create(newdfd, to, &path, lookup_flags);
 	error = PTR_ERR(dentry);
 	if (IS_ERR(dentry))
-		goto out_putname;
+		goto out_putfrom;
 
 	error = security_path_symlink(&path, dentry, from->name);
 	if (!error) {
@@ -4222,7 +4222,9 @@ static long do_symlinkat(const char __user *oldname, int newdfd,
 		lookup_flags |= LOOKUP_REVAL;
 		goto retry;
 	}
-out_putname:
+out_putboth:
+	putname(to);
+out_putfrom:
 	putname(from);
 	return error;
 }
@@ -4230,12 +4232,12 @@ static long do_symlinkat(const char __user *oldname, int newdfd,
 SYSCALL_DEFINE3(symlinkat, const char __user *, oldname,
 		int, newdfd, const char __user *, newname)
 {
-	return do_symlinkat(oldname, newdfd, newname);
+	return do_symlinkat(getname(oldname), newdfd, getname(newname));
 }
 
 SYSCALL_DEFINE2(symlink, const char __user *, oldname, const char __user *, newname)
 {
-	return do_symlinkat(oldname, AT_FDCWD, newname);
+	return do_symlinkat(getname(oldname), AT_FDCWD, getname(newname));
 }
 
 /**
-- 
2.30.2

[PATCH v7 06/10] namei: add getname_uflags()

[Dmitry Kadashev]

There are a couple of places where we already open-code the (flags &
AT_EMPTY_PATH) check and io_uring will likely add another one in the
future.  Let's just add a simple helper getname_uflags() that handles
this directly and use it.

Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <christian.brauner@ubuntu.com>
Link: https://lore.kernel.org/io-uring/20210415100815.edrn4a7cy26wkowe@wittgenstein/
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Dmitry Kadashev <dkadashev@gmail.com>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
---
 fs/exec.c          | 8 ++------
 fs/namei.c         | 8 ++++++++
 include/linux/fs.h | 1 +
 3 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index 18594f11c31f..df33ecaf2111 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -2069,10 +2069,8 @@ SYSCALL_DEFINE5(execveat,
 		const char __user *const __user *, envp,
 		int, flags)
 {
-	int lookup_flags = (flags & AT_EMPTY_PATH) ? LOOKUP_EMPTY : 0;
-
 	return do_execveat(fd,
-			   getname_flags(filename, lookup_flags, NULL),
+			   getname_uflags(filename, flags),
 			   argv, envp, flags);
 }
 
@@ -2090,10 +2088,8 @@ COMPAT_SYSCALL_DEFINE5(execveat, int, fd,
 		       const compat_uptr_t __user *, envp,
 		       int,  flags)
 {
-	int lookup_flags = (flags & AT_EMPTY_PATH) ? LOOKUP_EMPTY : 0;
-
 	return compat_do_execveat(fd,
-				  getname_flags(filename, lookup_flags, NULL),
+				  getname_uflags(filename, flags),
 				  argv, envp, flags);
 }
 #endif
diff --git a/fs/namei.c b/fs/namei.c
index 57170d57e84d..70a3c5124db3 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -203,6 +203,14 @@ getname_flags(const char __user *filename, int flags, int *empty)
 	return result;
 }
 
+struct filename *
+getname_uflags(const char __user *filename, int uflags)
+{
+	int flags = (uflags & AT_EMPTY_PATH) ? LOOKUP_EMPTY : 0;
+
+	return getname_flags(filename, flags, NULL);
+}
+
 struct filename *
 getname(const char __user * filename)
 {
diff --git a/include/linux/fs.h b/include/linux/fs.h
index c3c88fdb9b2a..5885a68d2c12 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2781,6 +2781,7 @@ static inline struct file *file_clone_open(struct file *file)
 extern int filp_close(struct file *, fl_owner_t id);
 
 extern struct filename *getname_flags(const char __user *, int, int *);
+extern struct filename *getname_uflags(const char __user *, int);
 extern struct filename *getname(const char __user *);
 extern struct filename *getname_kernel(const char *);
 extern void putname(struct filename *name);
-- 
2.30.2

[PATCH v7 07/10] fs: make do_linkat() take struct filename

[Dmitry Kadashev]

Pass in the struct filename pointers instead of the user string, for
uniformity with do_renameat2, do_unlinkat, do_mknodat, etc.

Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <christian.brauner@ubuntu.com>
Link: https://lore.kernel.org/io-uring/20210330071700.kpjoyp5zlni7uejm@wittgenstein/
Signed-off-by: Dmitry Kadashev <dkadashev@gmail.com>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
---
 fs/namei.c | 57 +++++++++++++++++++++++++++++++++++++-----------------
 1 file changed, 39 insertions(+), 18 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 70a3c5124db3..0a2731f7ef71 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2450,7 +2450,7 @@ static int path_lookupat(struct nameidata *nd, unsigned flags, struct path *path
 	return err;
 }
 
-int filename_lookup(int dfd, struct filename *name, unsigned flags,
+static int __filename_lookup(int dfd, struct filename *name, unsigned flags,
 		    struct path *path, struct path *root)
 {
 	int retval;
@@ -2472,7 +2472,18 @@ int filename_lookup(int dfd, struct filename *name, unsigned flags,
 		audit_inode(name, path->dentry,
 			    flags & LOOKUP_MOUNTPOINT ? AUDIT_INODE_NOEVAL : 0);
 	restore_nameidata();
-	putname(name);
+	if (retval)
+		putname(name);
+	return retval;
+}
+
+int filename_lookup(int dfd, struct filename *name, unsigned flags,
+		    struct path *path, struct path *root)
+{
+	int retval = __filename_lookup(dfd, name, flags, path, root);
+
+	if (!retval)
+		putname(name);
 	return retval;
 }
 
@@ -4346,8 +4357,8 @@ EXPORT_SYMBOL(vfs_link);
  * with linux 2.0, and to avoid hard-linking to directories
  * and other special files.  --ADM
  */
-static int do_linkat(int olddfd, const char __user *oldname, int newdfd,
-	      const char __user *newname, int flags)
+static int do_linkat(int olddfd, struct filename *old, int newdfd,
+	      struct filename *new, int flags)
 {
 	struct user_namespace *mnt_userns;
 	struct dentry *new_dentry;
@@ -4356,31 +4367,36 @@ static int do_linkat(int olddfd, const char __user *oldname, int newdfd,
 	int how = 0;
 	int error;
 
-	if ((flags & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH)) != 0)
-		return -EINVAL;
+	if ((flags & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH)) != 0) {
+		error = -EINVAL;
+		goto out_putnames;
+	}
 	/*
 	 * To use null names we require CAP_DAC_READ_SEARCH
 	 * This ensures that not everyone will be able to create
 	 * handlink using the passed filedescriptor.
 	 */
-	if (flags & AT_EMPTY_PATH) {
-		if (!capable(CAP_DAC_READ_SEARCH))
-			return -ENOENT;
-		how = LOOKUP_EMPTY;
+	if (flags & AT_EMPTY_PATH && !capable(CAP_DAC_READ_SEARCH)) {
+		error = -ENOENT;
+		goto out_putnames;
 	}
 
 	if (flags & AT_SYMLINK_FOLLOW)
 		how |= LOOKUP_FOLLOW;
 retry:
-	error = user_path_at(olddfd, oldname, how, &old_path);
+	error = __filename_lookup(olddfd, old, how, &old_path, NULL);
 	if (error)
-		return error;
+		goto out_putnew;
 
-	new_dentry = user_path_create(newdfd, newname, &new_path,
+	new_dentry = __filename_create(newdfd, new, &new_path,
 					(how & LOOKUP_REVAL));
 	error = PTR_ERR(new_dentry);
-	if (IS_ERR(new_dentry))
-		goto out;
+	if (IS_ERR(new_dentry)) {
+		// On error `new` is freed by __filename_create, set to NULL to
+		// signal that we do not have to free it below
+		new = NULL;
+		goto out_putpath;
+	}
 
 	error = -EXDEV;
 	if (old_path.mnt != new_path.mnt)
@@ -4408,8 +4424,12 @@ static int do_linkat(int olddfd, const char __user *oldname, int newdfd,
 		how |= LOOKUP_REVAL;
 		goto retry;
 	}
-out:
+out_putpath:
 	path_put(&old_path);
+out_putnames:
+	putname(old);
+out_putnew:
+	putname(new);
 
 	return error;
 }
@@ -4417,12 +4437,13 @@ static int do_linkat(int olddfd, const char __user *oldname, int newdfd,
 SYSCALL_DEFINE5(linkat, int, olddfd, const char __user *, oldname,
 		int, newdfd, const char __user *, newname, int, flags)
 {
-	return do_linkat(olddfd, oldname, newdfd, newname, flags);
+	return do_linkat(olddfd, getname_uflags(oldname, flags),
+		newdfd, getname(newname), flags);
 }
 
 SYSCALL_DEFINE2(link, const char __user *, oldname, const char __user *, newname)
 {
-	return do_linkat(AT_FDCWD, oldname, AT_FDCWD, newname, 0);
+	return do_linkat(AT_FDCWD, getname(oldname), AT_FDCWD, getname(newname), 0);
 }
 
 /**
-- 
2.30.2

[PATCH v7 08/10] fs: update do_*() helpers to return ints

[Dmitry Kadashev]

Update the following to return int rather than long, for uniformity with
the rest of the do_* helpers in namei.c:

* do_rmdir()
* do_unlinkat()
* do_mkdirat()
* do_mknodat()
* do_symlinkat()

Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <christian.brauner@ubuntu.com>
Link: https://lore.kernel.org/io-uring/20210514143202.dmzfcgz5hnauy7ze@wittgenstein/
Signed-off-by: Dmitry Kadashev <dkadashev@gmail.com>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
---
 fs/internal.h |  6 +++---
 fs/namei.c    | 10 +++++-----
 2 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/fs/internal.h b/fs/internal.h
index 848e165ef0f1..207a455e32d3 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -72,12 +72,12 @@ extern int filename_lookup(int dfd, struct filename *name, unsigned flags,
 			   struct path *path, struct path *root);
 extern int vfs_path_lookup(struct dentry *, struct vfsmount *,
 			   const char *, unsigned int, struct path *);
-long do_rmdir(int dfd, struct filename *name);
-long do_unlinkat(int dfd, struct filename *name);
+int do_rmdir(int dfd, struct filename *name);
+int do_unlinkat(int dfd, struct filename *name);
 int may_linkat(struct user_namespace *mnt_userns, struct path *link);
 int do_renameat2(int olddfd, struct filename *oldname, int newdfd,
 		 struct filename *newname, unsigned int flags);
-long do_mkdirat(int dfd, struct filename *name, umode_t mode);
+int do_mkdirat(int dfd, struct filename *name, umode_t mode);
 
 /*
  * namespace.c
diff --git a/fs/namei.c b/fs/namei.c
index 0a2731f7ef71..1656073ca493 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -3746,7 +3746,7 @@ static int may_mknod(umode_t mode)
 	}
 }
 
-static long do_mknodat(int dfd, struct filename *name, umode_t mode,
+static int do_mknodat(int dfd, struct filename *name, umode_t mode,
 		unsigned int dev)
 {
 	struct user_namespace *mnt_userns;
@@ -3850,7 +3850,7 @@ int vfs_mkdir(struct user_namespace *mnt_userns, struct inode *dir,
 }
 EXPORT_SYMBOL(vfs_mkdir);
 
-long do_mkdirat(int dfd, struct filename *name, umode_t mode)
+int do_mkdirat(int dfd, struct filename *name, umode_t mode)
 {
 	struct dentry *dentry;
 	struct path path;
@@ -3945,7 +3945,7 @@ int vfs_rmdir(struct user_namespace *mnt_userns, struct inode *dir,
 }
 EXPORT_SYMBOL(vfs_rmdir);
 
-long do_rmdir(int dfd, struct filename *name)
+int do_rmdir(int dfd, struct filename *name)
 {
 	struct user_namespace *mnt_userns;
 	int error = 0;
@@ -4083,7 +4083,7 @@ EXPORT_SYMBOL(vfs_unlink);
  * writeout happening, and we don't want to prevent access to the directory
  * while waiting on the I/O.
  */
-long do_unlinkat(int dfd, struct filename *name)
+int do_unlinkat(int dfd, struct filename *name)
 {
 	int error;
 	struct dentry *dentry;
@@ -4210,7 +4210,7 @@ int vfs_symlink(struct user_namespace *mnt_userns, struct inode *dir,
 }
 EXPORT_SYMBOL(vfs_symlink);
 
-static long do_symlinkat(struct filename *from, int newdfd,
+static int do_symlinkat(struct filename *from, int newdfd,
 		  struct filename *to)
 {
 	int error;
-- 
2.30.2

[PATCH v7 09/10] io_uring: add support for IORING_OP_SYMLINKAT

[Dmitry Kadashev]

IORING_OP_SYMLINKAT behaves like symlinkat(2) and takes the same flags
and arguments.

Cc: Linus Torvalds <torvalds@linux-foundation.org>
Suggested-by: Christian Brauner <christian.brauner@ubuntu.com>
Link: https://lore.kernel.org/io-uring/20210514145259.wtl4xcsp52woi6ab@wittgenstein/
Signed-off-by: Dmitry Kadashev <dkadashev@gmail.com>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
---
 fs/internal.h                 |  1 +
 fs/io_uring.c                 | 66 +++++++++++++++++++++++++++++++++++
 fs/namei.c                    |  3 +-
 include/uapi/linux/io_uring.h |  1 +
 4 files changed, 69 insertions(+), 2 deletions(-)

diff --git a/fs/internal.h b/fs/internal.h
index 207a455e32d3..3b3954214385 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -78,6 +78,7 @@ int may_linkat(struct user_namespace *mnt_userns, struct path *link);
 int do_renameat2(int olddfd, struct filename *oldname, int newdfd,
 		 struct filename *newname, unsigned int flags);
 int do_mkdirat(int dfd, struct filename *name, umode_t mode);
+int do_symlinkat(struct filename *from, int newdfd, struct filename *to);
 
 /*
  * namespace.c
diff --git a/fs/io_uring.c b/fs/io_uring.c
index 42d54f9bbbb2..a0f681ec25bb 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -681,6 +681,13 @@ struct io_mkdir {
 	struct filename			*filename;
 };
 
+struct io_symlink {
+	struct file			*file;
+	int				new_dfd;
+	struct filename			*oldpath;
+	struct filename			*newpath;
+};
+
 struct io_completion {
 	struct file			*file;
 	struct list_head		list;
@@ -839,6 +846,7 @@ struct io_kiocb {
 		struct io_rename	rename;
 		struct io_unlink	unlink;
 		struct io_mkdir		mkdir;
+		struct io_symlink	symlink;
 		/* use only after cleaning per-op data, see io_clean_op() */
 		struct io_completion	compl;
 	};
@@ -1051,6 +1059,7 @@ static const struct io_op_def io_op_defs[] = {
 	[IORING_OP_RENAMEAT] = {},
 	[IORING_OP_UNLINKAT] = {},
 	[IORING_OP_MKDIRAT] = {},
+	[IORING_OP_SYMLINKAT] = {},
 };
 
 static bool io_disarm_next(struct io_kiocb *req);
@@ -3596,6 +3605,54 @@ static int io_mkdirat(struct io_kiocb *req, int issue_flags)
 	return 0;
 }
 
+static int io_symlinkat_prep(struct io_kiocb *req,
+			    const struct io_uring_sqe *sqe)
+{
+	struct io_symlink *sl = &req->symlink;
+	const char __user *oldpath, *newpath;
+
+	if (unlikely(req->ctx->flags & IORING_SETUP_IOPOLL))
+		return -EINVAL;
+	if (sqe->ioprio || sqe->len || sqe->rw_flags || sqe->buf_index)
+		return -EINVAL;
+	if (unlikely(req->flags & REQ_F_FIXED_FILE))
+		return -EBADF;
+
+	sl->new_dfd = READ_ONCE(sqe->fd);
+	oldpath = u64_to_user_ptr(READ_ONCE(sqe->addr));
+	newpath = u64_to_user_ptr(READ_ONCE(sqe->addr2));
+
+	sl->oldpath = getname(oldpath);
+	if (IS_ERR(sl->oldpath))
+		return PTR_ERR(sl->oldpath);
+
+	sl->newpath = getname(newpath);
+	if (IS_ERR(sl->newpath)) {
+		putname(sl->oldpath);
+		return PTR_ERR(sl->newpath);
+	}
+
+	req->flags |= REQ_F_NEED_CLEANUP;
+	return 0;
+}
+
+static int io_symlinkat(struct io_kiocb *req, int issue_flags)
+{
+	struct io_symlink *sl = &req->symlink;
+	int ret;
+
+	if (issue_flags & IO_URING_F_NONBLOCK)
+		return -EAGAIN;
+
+	ret = do_symlinkat(sl->oldpath, sl->new_dfd, sl->newpath);
+
+	req->flags &= ~REQ_F_NEED_CLEANUP;
+	if (ret < 0)
+		req_set_fail(req);
+	io_req_complete(req, ret);
+	return 0;
+}
+
 static int io_shutdown_prep(struct io_kiocb *req,
 			    const struct io_uring_sqe *sqe)
 {
@@ -6006,6 +6063,8 @@ static int io_req_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 		return io_unlinkat_prep(req, sqe);
 	case IORING_OP_MKDIRAT:
 		return io_mkdirat_prep(req, sqe);
+	case IORING_OP_SYMLINKAT:
+		return io_symlinkat_prep(req, sqe);
 	}
 
 	printk_once(KERN_WARNING "io_uring: unhandled opcode %d\n",
@@ -6170,6 +6229,10 @@ static void io_clean_op(struct io_kiocb *req)
 		case IORING_OP_MKDIRAT:
 			putname(req->mkdir.filename);
 			break;
+		case IORING_OP_SYMLINKAT:
+			putname(req->symlink.oldpath);
+			putname(req->symlink.newpath);
+			break;
 		}
 	}
 	if ((req->flags & REQ_F_POLLED) && req->apoll) {
@@ -6301,6 +6364,9 @@ static int io_issue_sqe(struct io_kiocb *req, unsigned int issue_flags)
 	case IORING_OP_MKDIRAT:
 		ret = io_mkdirat(req, issue_flags);
 		break;
+	case IORING_OP_SYMLINKAT:
+		ret = io_symlinkat(req, issue_flags);
+		break;
 	default:
 		ret = -EINVAL;
 		break;
diff --git a/fs/namei.c b/fs/namei.c
index 1656073ca493..3cf8f5e3b155 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -4210,8 +4210,7 @@ int vfs_symlink(struct user_namespace *mnt_userns, struct inode *dir,
 }
 EXPORT_SYMBOL(vfs_symlink);
 
-static int do_symlinkat(struct filename *from, int newdfd,
-		  struct filename *to)
+int do_symlinkat(struct filename *from, int newdfd, struct filename *to)
 {
 	int error;
 	struct dentry *dentry;
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index a926407c230e..61fd347ab176 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -134,6 +134,7 @@ enum {
 	IORING_OP_RENAMEAT,
 	IORING_OP_UNLINKAT,
 	IORING_OP_MKDIRAT,
+	IORING_OP_SYMLINKAT,
 
 	/* this goes last, obviously */
 	IORING_OP_LAST,
-- 
2.30.2

[PATCH v7 10/10] io_uring: add support for IORING_OP_LINKAT

[Dmitry Kadashev]

IORING_OP_LINKAT behaves like linkat(2) and takes the same flags and
arguments.

In some internal places 'hardlink' is used instead of 'link' to avoid
confusion with the SQE links. Name 'link' conflicts with the existing
'link' member of io_kiocb.

Cc: Linus Torvalds <torvalds@linux-foundation.org>
Suggested-by: Christian Brauner <christian.brauner@ubuntu.com>
Link: https://lore.kernel.org/io-uring/20210514145259.wtl4xcsp52woi6ab@wittgenstein/
Signed-off-by: Dmitry Kadashev <dkadashev@gmail.com>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
---
 fs/internal.h                 |  2 +
 fs/io_uring.c                 | 71 +++++++++++++++++++++++++++++++++++
 fs/namei.c                    |  2 +-
 include/uapi/linux/io_uring.h |  2 +
 4 files changed, 76 insertions(+), 1 deletion(-)

diff --git a/fs/internal.h b/fs/internal.h
index 3b3954214385..15a7d210cc67 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -79,6 +79,8 @@ int do_renameat2(int olddfd, struct filename *oldname, int newdfd,
 		 struct filename *newname, unsigned int flags);
 int do_mkdirat(int dfd, struct filename *name, umode_t mode);
 int do_symlinkat(struct filename *from, int newdfd, struct filename *to);
+int do_linkat(int olddfd, struct filename *old, int newdfd,
+			struct filename *new, int flags);
 
 /*
  * namespace.c
diff --git a/fs/io_uring.c b/fs/io_uring.c
index a0f681ec25bb..d18ca8afd1fb 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -688,6 +688,15 @@ struct io_symlink {
 	struct filename			*newpath;
 };
 
+struct io_hardlink {
+	struct file			*file;
+	int				old_dfd;
+	int				new_dfd;
+	struct filename			*oldpath;
+	struct filename			*newpath;
+	int				flags;
+};
+
 struct io_completion {
 	struct file			*file;
 	struct list_head		list;
@@ -847,6 +856,7 @@ struct io_kiocb {
 		struct io_unlink	unlink;
 		struct io_mkdir		mkdir;
 		struct io_symlink	symlink;
+		struct io_hardlink	hardlink;
 		/* use only after cleaning per-op data, see io_clean_op() */
 		struct io_completion	compl;
 	};
@@ -1060,6 +1070,7 @@ static const struct io_op_def io_op_defs[] = {
 	[IORING_OP_UNLINKAT] = {},
 	[IORING_OP_MKDIRAT] = {},
 	[IORING_OP_SYMLINKAT] = {},
+	[IORING_OP_LINKAT] = {},
 };
 
 static bool io_disarm_next(struct io_kiocb *req);
@@ -3653,6 +3664,57 @@ static int io_symlinkat(struct io_kiocb *req, int issue_flags)
 	return 0;
 }
 
+static int io_linkat_prep(struct io_kiocb *req,
+			    const struct io_uring_sqe *sqe)
+{
+	struct io_hardlink *lnk = &req->hardlink;
+	const char __user *oldf, *newf;
+
+	if (unlikely(req->ctx->flags & IORING_SETUP_IOPOLL))
+		return -EINVAL;
+	if (sqe->ioprio || sqe->rw_flags || sqe->buf_index)
+		return -EINVAL;
+	if (unlikely(req->flags & REQ_F_FIXED_FILE))
+		return -EBADF;
+
+	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);
+
+	lnk->oldpath = getname(oldf);
+	if (IS_ERR(lnk->oldpath))
+		return PTR_ERR(lnk->oldpath);
+
+	lnk->newpath = getname(newf);
+	if (IS_ERR(lnk->newpath)) {
+		putname(lnk->oldpath);
+		return PTR_ERR(lnk->newpath);
+	}
+
+	req->flags |= REQ_F_NEED_CLEANUP;
+	return 0;
+}
+
+static int io_linkat(struct io_kiocb *req, int issue_flags)
+{
+	struct io_hardlink *lnk = &req->hardlink;
+	int ret;
+
+	if (issue_flags & IO_URING_F_NONBLOCK)
+		return -EAGAIN;
+
+	ret = do_linkat(lnk->old_dfd, lnk->oldpath, lnk->new_dfd,
+				lnk->newpath, lnk->flags);
+
+	req->flags &= ~REQ_F_NEED_CLEANUP;
+	if (ret < 0)
+		req_set_fail(req);
+	io_req_complete(req, ret);
+	return 0;
+}
+
 static int io_shutdown_prep(struct io_kiocb *req,
 			    const struct io_uring_sqe *sqe)
 {
@@ -6065,6 +6127,8 @@ static int io_req_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 		return io_mkdirat_prep(req, sqe);
 	case IORING_OP_SYMLINKAT:
 		return io_symlinkat_prep(req, sqe);
+	case IORING_OP_LINKAT:
+		return io_linkat_prep(req, sqe);
 	}
 
 	printk_once(KERN_WARNING "io_uring: unhandled opcode %d\n",
@@ -6233,6 +6297,10 @@ static void io_clean_op(struct io_kiocb *req)
 			putname(req->symlink.oldpath);
 			putname(req->symlink.newpath);
 			break;
+		case IORING_OP_LINKAT:
+			putname(req->hardlink.oldpath);
+			putname(req->hardlink.newpath);
+			break;
 		}
 	}
 	if ((req->flags & REQ_F_POLLED) && req->apoll) {
@@ -6367,6 +6435,9 @@ static int io_issue_sqe(struct io_kiocb *req, unsigned int issue_flags)
 	case IORING_OP_SYMLINKAT:
 		ret = io_symlinkat(req, issue_flags);
 		break;
+	case IORING_OP_LINKAT:
+		ret = io_linkat(req, issue_flags);
+		break;
 	default:
 		ret = -EINVAL;
 		break;
diff --git a/fs/namei.c b/fs/namei.c
index 3cf8f5e3b155..99d315462c42 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -4356,7 +4356,7 @@ EXPORT_SYMBOL(vfs_link);
  * with linux 2.0, and to avoid hard-linking to directories
  * and other special files.  --ADM
  */
-static int do_linkat(int olddfd, struct filename *old, int newdfd,
+int do_linkat(int olddfd, struct filename *old, int newdfd,
 	      struct filename *new, int flags)
 {
 	struct user_namespace *mnt_userns;
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 61fd347ab176..10eb38d2864f 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -44,6 +44,7 @@ struct io_uring_sqe {
 		__u32		splice_flags;
 		__u32		rename_flags;
 		__u32		unlink_flags;
+		__u32		hardlink_flags;
 	};
 	__u64	user_data;	/* data to be passed back at completion time */
 	/* pack this to avoid bogus arm OABI complaints */
@@ -135,6 +136,7 @@ enum {
 	IORING_OP_UNLINKAT,
 	IORING_OP_MKDIRAT,
 	IORING_OP_SYMLINKAT,
+	IORING_OP_LINKAT,
 
 	/* this goes last, obviously */
 	IORING_OP_LAST,
-- 
2.30.2

Re: [PATCH v7 07/10] fs: make do_linkat() take struct filename

[Linus Torvalds]

On Tue, Jul 6, 2021 at 5:49 AM Dmitry Kadashev <dkadashev@gmail.com> wrote:
>
> Pass in the struct filename pointers instead of the user string, for
> uniformity with do_renameat2, do_unlinkat, do_mknodat, etc.

This is the only one in the series that I still react fairly negatively at.

I still just don't like how filename_lookup() used to be nice and easy
to understand ("always eat the name"), and while those semantics
remain, the new __filename_lookup() has those odd semantics of only
eating it on failure.

And there is exactly _one_ caller of that new __filename_lookup(), and it does

        error = __filename_lookup(olddfd, old, how, &old_path, NULL);
        if (error)
                goto out_putnew;

and I don't even understand why you'd want to eat it on error, because
if if *didn't* eat it on error, it would just do

        error = __filename_lookup(olddfd, old, how, &old_path, NULL);
        if (error)
                goto out_putnames;

and it would be much easier to understand (and the "out_putnew" label
would go away entirely)

What am I missing? You had some reason for not eating the name
unconditionally, but I look at this patch and I just don't see it.

              Linus

Re: [PATCH v7 07/10] fs: make do_linkat() take struct filename

[Dmitry Kadashev]

On Wed, Jul 7, 2021 at 1:05 AM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> This is the only one in the series that I still react fairly negatively at.
>
> I still just don't like how filename_lookup() used to be nice and easy
> to understand ("always eat the name"), and while those semantics
> remain, the new __filename_lookup() has those odd semantics of only
> eating it on failure.
>
> And there is exactly _one_ caller of that new __filename_lookup(), and it does
>
>         error = __filename_lookup(olddfd, old, how, &old_path, NULL);
>         if (error)
>                 goto out_putnew;
>
> and I don't even understand why you'd want to eat it on error, because
> if if *didn't* eat it on error, it would just do
>
>         error = __filename_lookup(olddfd, old, how, &old_path, NULL);
>         if (error)
>                 goto out_putnames;
>
> and it would be much easier to understand (and the "out_putnew" label
> would go away entirely)
>
> What am I missing? You had some reason for not eating the name
> unconditionally, but I look at this patch and I just don't see it.

__filename_lookup() does that "eat the name on error" for uniformity
with the __filename_create(), and the latter does that mostly because Al
suggested to do it that way:

https://lore.kernel.org/io-uring/20210201150042.GQ740243@zeniv-ca/

Granted, he did that back when this series was much smaller, only about
mkdirat, and in that case it looked like it makes things a tad simpler,
and even though I found the semantics a bit confusing, I've assumed that
I'm missing something and this is something the FS code does, so people
are used to it.

Anyway, I'll send v8 of this series with yet another preparation patch,
that will change filename_parenat() to return an error code instead of
struct filename *, and split it into two: filename_parenat() that always
eats the name, and __filename_parentat() that never eats the name. And
__filename_lookup() and __filename_create() will never eat the name as
well, so things are nice and uniform and easy to reason about.

And hopefully if Al does not like that approach he can weigh in.

-- 
Dmitry Kadashev