Add new fcntl F_GET_MAX_WRITE_STREAMS.
This returns the numbers of streams that are available for userspace.
And for that, use ->user_write_streams() callback when the involved
filesystem provides it.
In absence of such callback, use 'max_write_streams' queue limit of the
underlying block device.
Signed-off-by: Kanchan Joshi <joshi.k@xxxxxxxxxxx>
---
fs/fcntl.c | 31 +++++++++++++++++++++++++++++++
include/uapi/linux/fcntl.h | 5 +++++
2 files changed, 36 insertions(+)
diff --git a/fs/fcntl.c b/fs/fcntl.c
index 5598e4d57422..36ca833e9a0b 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -27,6 +27,7 @@
#include <linux/compat.h>
#include <linux/mount.h>
#include <linux/rw_hint.h>
+#include <linux/blkdev.h>
#include <linux/poll.h>
#include <asm/siginfo.h>
@@ -394,6 +395,33 @@ static long fcntl_set_rw_hint(struct file *file, unsigned int cmd,
return 0;
}
+static u8 vfs_user_write_streams(struct inode *inode)
+{
+ struct super_block *sb;
+
+ if (S_ISBLK(inode->i_mode))
+ return bdev_max_write_streams(I_BDEV(inode));
+
+ sb = inode->i_sb;
+ /* If available, use per-mount/fs policy */
+ if (sb->s_op && sb->s_op->user_write_streams)
+ return sb->s_op->user_write_streams(sb);
+ /* otherwise, fallback to queue limit */
+ if (sb->s_bdev)
+ return bdev_max_write_streams(sb->s_bdev);
+ return 0;
+}
+
+static long fcntl_get_max_write_streams(struct file *file)
+{
+ struct inode *inode = file_inode(file);
+
+ if (S_ISBLK(inode->i_mode))
+ inode = file->f_mapping->host;
+
+ return vfs_user_write_streams(inode);
+}
+
/* Is the file descriptor a dup of the file? */
static long f_dupfd_query(int fd, struct file *filp)
{
@@ -552,6 +580,9 @@ static long do_fcntl(int fd, unsigned int cmd, unsigned long arg,
case F_SET_RW_HINT:
err = fcntl_set_rw_hint(filp, cmd, arg);
break;
+ case F_GET_MAX_WRITE_STREAMS:
+ err = fcntl_get_max_write_streams(filp);
+ break;
default:
break;
}
diff --git a/include/uapi/linux/fcntl.h b/include/uapi/linux/fcntl.h
index f291ab4f94eb..87ec808d0f03 100644
--- a/include/uapi/linux/fcntl.h
+++ b/include/uapi/linux/fcntl.h
@@ -61,6 +61,11 @@
#define F_GET_FILE_RW_HINT (F_LINUX_SPECIFIC_BASE + 13)
#define F_SET_FILE_RW_HINT (F_LINUX_SPECIFIC_BASE + 14)
+/*
+ * Query available write streams
+ */
+#define F_GET_MAX_WRITE_STREAMS (F_LINUX_SPECIFIC_BASE + 15)
+
/*
* Valid hint values for F_{GET,SET}_RW_HINT. 0 is "not set", or can be
* used to clear any hints previously set.
--
2.25.1
