Add two new fcntls:
F_GET_WRITE_STREAM - to query the write-stream on inode
F_SET_WRITE_STREAM - to set the write-stream on inode
Application should query the available streams by calling
F_GET_MAX_WRITE_STREAMS first.
If returned value is N, applications can choose any value from 1 to N
while setting the stream.
Setting the value 0 is not flagged as an error as that implies no
stream.
But setting a larger value than available streams is rejected.
Signed-off-by: Kanchan Joshi <joshi.k@xxxxxxxxxxx>
---
fs/fcntl.c | 33 +++++++++++++++++++++++++++++++++
include/uapi/linux/fcntl.h | 2 ++
2 files changed, 35 insertions(+)
diff --git a/fs/fcntl.c b/fs/fcntl.c
index 36ca833e9a0b..ce89393f8dbf 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -422,6 +422,33 @@ static long fcntl_get_max_write_streams(struct file *file)
return vfs_user_write_streams(inode);
}
+static long fcntl_get_write_stream(struct file *file)
+{
+ struct inode *inode = file_inode(file);
+
+ if (S_ISBLK(inode->i_mode))
+ inode = file->f_mapping->host;
+
+ return inode->i_write_stream;
+}
+
+static long fcntl_set_write_stream(struct file *file, unsigned long arg)
+{
+ struct inode *inode = file_inode(file);
+
+ if (!inode_owner_or_capable(file_mnt_idmap(file), inode))
+ return -EPERM;
+
+ if (S_ISBLK(inode->i_mode))
+ inode = file->f_mapping->host;
+
+ if (arg > vfs_user_write_streams(inode))
+ return -EINVAL;
+
+ WRITE_ONCE(inode->i_write_stream, arg);
+ return 0;
+}
+
/* Is the file descriptor a dup of the file? */
static long f_dupfd_query(int fd, struct file *filp)
{
@@ -583,6 +610,12 @@ static long do_fcntl(int fd, unsigned int cmd, unsigned long arg,
case F_GET_MAX_WRITE_STREAMS:
err = fcntl_get_max_write_streams(filp);
break;
+ case F_GET_WRITE_STREAM:
+ err = fcntl_get_write_stream(filp);
+ break;
+ case F_SET_WRITE_STREAM:
+ err = fcntl_set_write_stream(filp, arg);
+ break;
default:
break;
}
diff --git a/include/uapi/linux/fcntl.h b/include/uapi/linux/fcntl.h
index 87ec808d0f03..dd3c498515ce 100644
--- a/include/uapi/linux/fcntl.h
+++ b/include/uapi/linux/fcntl.h
@@ -65,6 +65,8 @@
* Query available write streams
*/
#define F_GET_MAX_WRITE_STREAMS (F_LINUX_SPECIFIC_BASE + 15)
+#define F_GET_WRITE_STREAM (F_LINUX_SPECIFIC_BASE + 16)
+#define F_SET_WRITE_STREAM (F_LINUX_SPECIFIC_BASE + 17)
/*
* Valid hint values for F_{GET,SET}_RW_HINT. 0 is "not set", or can be
--
2.25.1
