Merge tag 'stream_open-5.2' of https://lab.nexedi.com/kirr/linux

Pull stream_open conversion from Kirill Smelkov:

 - remove unnecessary double nonseekable_open from drivers/char/dtlk.c
   as noticed by Pavel Machek while reviewing nonseekable_open ->
   stream_open mass conversion.

 - the mass conversion patch promised in commit 10dce8af3422 ("fs:
   stream_open - opener for stream-like files so that read and write can
   run simultaneously without deadlock") and is automatically generated
   by running

        $ make coccicheck MODE=patch COCCI=scripts/coccinelle/api/stream_open.cocci

   I've verified each generated change manually - that it is correct to
   convert - and each other nonseekable_open instance left - that it is
   either not correct to convert there, or that it is not converted due
   to current stream_open.cocci limitations. More details on this in the
   patch.

 - finally, change VFS to pass ppos=NULL into .read/.write for files
   that declare themselves streams. It was suggested by Rasmus Villemoes
   and makes sure that if ppos starts to be erroneously used in a stream
   file, such bug won't go unnoticed and will produce an oops instead of
   creating illusion of position change being taken into account.

   Note: this patch does not conflict with "fuse: Add FOPEN_STREAM to
   use stream_open()" that will be hopefully coming via FUSE tree,
   because fs/fuse/ uses new-style .read_iter/.write_iter, and for these
   accessors position is still passed as non-pointer kiocb.ki_pos .

* tag 'stream_open-5.2' of https://lab.nexedi.com/kirr/linux:
  vfs: pass ppos=NULL to .read()/.write() of FMODE_STREAM files
  *: convert stream-like files from nonseekable_open -> stream_open
  dtlk: remove double call to nonseekable_open

2 files changed, 70 insertions, 48 deletions

diff --git a/fs/open.c b/fs/open.c
index a00350018a47..9c7d724a6f67 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -1219,8 +1219,9 @@ EXPORT_SYMBOL(nonseekable_open);
 /*
  * stream_open is used by subsystems that want stream-like file descriptors.
  * Such file descriptors are not seekable and don't have notion of position
- * (file.f_pos is always 0). Contrary to file descriptors of other regular
- * files, .read() and .write() can run simultaneously.
+ * (file.f_pos is always 0 and ppos passed to .read()/.write() is always NULL).
+ * Contrary to file descriptors of other regular files, .read() and .write()
+ * can run simultaneously.
  *
  * stream_open never fails and is marked to return int so that it could be
  * directly used as file_operations.open .
diff --git a/fs/read_write.c b/fs/read_write.c
index 61b43ad7608e..c543d965e288 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -365,29 +365,37 @@ out_putf:
 int rw_verify_area(int read_write, struct file *file, const loff_t *ppos, size_t count)
 {
 	struct inode *inode;
-	loff_t pos;
 	int retval = -EINVAL;
 
 	inode = file_inode(file);
 	if (unlikely((ssize_t) count < 0))
 		return retval;
-	pos = *ppos;
-	if (unlikely(pos < 0)) {
-		if (!unsigned_offsets(file))
-			return retval;
-		if (count >= -pos) /* both values are in 0..LLONG_MAX */
-			return -EOVERFLOW;
-	} else if (unlikely((loff_t) (pos + count) < 0)) {
-		if (!unsigned_offsets(file))
-			return retval;
-	}
 
-	if (unlikely(inode->i_flctx && mandatory_lock(inode))) {
-		retval = locks_mandatory_area(inode, file, pos, pos + count - 1,
-				read_write == READ ? F_RDLCK : F_WRLCK);
-		if (retval < 0)
-			return retval;
+	/*
+	 * ranged mandatory locking does not apply to streams - it makes sense
+	 * only for files where position has a meaning.
+	 */
+	if (ppos) {
+		loff_t pos = *ppos;
+
+		if (unlikely(pos < 0)) {
+			if (!unsigned_offsets(file))
+				return retval;
+			if (count >= -pos) /* both values are in 0..LLONG_MAX */
+				return -EOVERFLOW;
+		} else if (unlikely((loff_t) (pos + count) < 0)) {
+			if (!unsigned_offsets(file))
+				return retval;
+		}
+
+		if (unlikely(inode->i_flctx && mandatory_lock(inode))) {
+			retval = locks_mandatory_area(inode, file, pos, pos + count - 1,
+					read_write == READ ? F_RDLCK : F_WRLCK);
+			if (retval < 0)
+				return retval;
+		}
 	}
+
 	return security_file_permission(file,
 				read_write == READ ? MAY_READ : MAY_WRITE);
 }
@@ -400,12 +408,13 @@ static ssize_t new_sync_read(struct file *filp, char __user *buf, size_t len, lo
 	ssize_t ret;
 
 	init_sync_kiocb(&kiocb, filp);
-	kiocb.ki_pos = *ppos;
+	kiocb.ki_pos = (ppos ? *ppos : 0);
 	iov_iter_init(&iter, READ, &iov, 1, len);
 
 	ret = call_read_iter(filp, &kiocb, &iter);
 	BUG_ON(ret == -EIOCBQUEUED);
-	*ppos = kiocb.ki_pos;
+	if (ppos)
+		*ppos = kiocb.ki_pos;
 	return ret;
 }
 
@@ -468,12 +477,12 @@ static ssize_t new_sync_write(struct file *filp, const char __user *buf, size_t
 	ssize_t ret;
 
 	init_sync_kiocb(&kiocb, filp);
-	kiocb.ki_pos = *ppos;
+	kiocb.ki_pos = (ppos ? *ppos : 0);
 	iov_iter_init(&iter, WRITE, &iov, 1, len);
 
 	ret = call_write_iter(filp, &kiocb, &iter);
 	BUG_ON(ret == -EIOCBQUEUED);
-	if (ret > 0)
+	if (ret > 0 && ppos)
 		*ppos = kiocb.ki_pos;
 	return ret;
 }
@@ -558,15 +567,10 @@ ssize_t vfs_write(struct file *file, const char __user *buf, size_t count, loff_
 	return ret;
 }
 
-static inline loff_t file_pos_read(struct file *file)
-{
-	return file->f_mode & FMODE_STREAM ? 0 : file->f_pos;
-}
-
-static inline void file_pos_write(struct file *file, loff_t pos)
+/* file_ppos returns &file->f_pos or NULL if file is stream */
+static inline loff_t *file_ppos(struct file *file)
 {
-	if ((file->f_mode & FMODE_STREAM) == 0)
-		file->f_pos = pos;
+	return file->f_mode & FMODE_STREAM ? NULL : &file->f_pos;
 }
 
 ssize_t ksys_read(unsigned int fd, char __user *buf, size_t count)
@@ -575,10 +579,14 @@ ssize_t ksys_read(unsigned int fd, char __user *buf, size_t count)
 	ssize_t ret = -EBADF;
 
 	if (f.file) {
-		loff_t pos = file_pos_read(f.file);
-		ret = vfs_read(f.file, buf, count, &pos);
-		if (ret >= 0)
-			file_pos_write(f.file, pos);
+		loff_t pos, *ppos = file_ppos(f.file);
+		if (ppos) {
+			pos = *ppos;
+			ppos = &pos;
+		}
+		ret = vfs_read(f.file, buf, count, ppos);
+		if (ret >= 0 && ppos)
+			f.file->f_pos = pos;
 		fdput_pos(f);
 	}
 	return ret;
@@ -595,10 +603,14 @@ ssize_t ksys_write(unsigned int fd, const char __user *buf, size_t count)
 	ssize_t ret = -EBADF;
 
 	if (f.file) {
-		loff_t pos = file_pos_read(f.file);
-		ret = vfs_write(f.file, buf, count, &pos);
-		if (ret >= 0)
-			file_pos_write(f.file, pos);
+		loff_t pos, *ppos = file_ppos(f.file);
+		if (ppos) {
+			pos = *ppos;
+			ppos = &pos;
+		}
+		ret = vfs_write(f.file, buf, count, ppos);
+		if (ret >= 0 && ppos)
+			f.file->f_pos = pos;
 		fdput_pos(f);
 	}
 
@@ -673,14 +685,15 @@ static ssize_t do_iter_readv_writev(struct file *filp, struct iov_iter *iter,
 	ret = kiocb_set_rw_flags(&kiocb, flags);
 	if (ret)
 		return ret;
-	kiocb.ki_pos = *ppos;
+	kiocb.ki_pos = (ppos ? *ppos : 0);
 
 	if (type == READ)
 		ret = call_read_iter(filp, &kiocb, iter);
 	else
 		ret = call_write_iter(filp, &kiocb, iter);
 	BUG_ON(ret == -EIOCBQUEUED);
-	*ppos = kiocb.ki_pos;
+	if (ppos)
+		*ppos = kiocb.ki_pos;
 	return ret;
 }
 
@@ -1013,10 +1026,14 @@ static ssize_t do_readv(unsigned long fd, const struct iovec __user *vec,
 	ssize_t ret = -EBADF;
 
 	if (f.file) {
-		loff_t pos = file_pos_read(f.file);
-		ret = vfs_readv(f.file, vec, vlen, &pos, flags);
-		if (ret >= 0)
-			file_pos_write(f.file, pos);
+		loff_t pos, *ppos = file_ppos(f.file);
+		if (ppos) {
+			pos = *ppos;
+			ppos = &pos;
+		}
+		ret = vfs_readv(f.file, vec, vlen, ppos, flags);
+		if (ret >= 0 && ppos)
+			f.file->f_pos = pos;
 		fdput_pos(f);
 	}
 
@@ -1033,10 +1050,14 @@ static ssize_t do_writev(unsigned long fd, const struct iovec __user *vec,
 	ssize_t ret = -EBADF;
 
 	if (f.file) {
-		loff_t pos = file_pos_read(f.file);
-		ret = vfs_writev(f.file, vec, vlen, &pos, flags);
-		if (ret >= 0)
-			file_pos_write(f.file, pos);
+		loff_t pos, *ppos = file_ppos(f.file);
+		if (ppos) {
+			pos = *ppos;
+			ppos = &pos;
+		}
+		ret = vfs_writev(f.file, vec, vlen, ppos, flags);
+		if (ret >= 0 && ppos)
+			f.file->f_pos = pos;
 		fdput_pos(f);
 	}