Re: [PATCH 5/7] add llseek_nowait support for xfs

Hao Xu <hao.xu@xxxxxxxxx> · Thu, 27 Jul 2023 20:26:47 +0800

On 7/27/23 06:14, Dave Chinner wrote:
On Wed, Jul 26, 2023 at 06:26:01PM +0800, Hao Xu wrote:
From: Hao Xu <howeyxu@xxxxxxxxxxx>

Add llseek_nowait() operation for xfs, it acts just like llseek(). The
thing different is it delivers nowait parameter to iomap layer.

Signed-off-by: Hao Xu <howeyxu@xxxxxxxxxxx>
---
  fs/xfs/xfs_file.c | 29 +++++++++++++++++++++++++++--
  1 file changed, 27 insertions(+), 2 deletions(-)

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 73adc0aee2ff..cba82264221d 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -1257,10 +1257,11 @@ xfs_file_readdir(
  }
  
  STATIC loff_t
-xfs_file_llseek(
+__xfs_file_llseek(
  	struct file	*file,
  	loff_t		offset,
-	int		whence)
+	int		whence,
+	bool		nowait)
  {
  	struct inode		*inode = file->f_mapping->host;
  
@@ -1282,6 +1283,28 @@ xfs_file_llseek(
  	return vfs_setpos(file, offset, inode->i_sb->s_maxbytes);
  }
  
+STATIC loff_t
+xfs_file_llseek(
+	struct file	*file,
+	loff_t		offset,
+	int		whence)
+{
+	return __xfs_file_llseek(file, offset, whence, false);
+}
+
+STATIC loff_t
+xfs_file_llseek_nowait(
+	struct file	*file,
+	loff_t		offset,
+	int		whence,
+	bool		nowait)
+{
+	if (file->f_op == &xfs_file_operations)
+		return __xfs_file_llseek(file, offset, whence, nowait);
+	else
+		return generic_file_llseek(file, offset, whence);
+}
+
  #ifdef CONFIG_FS_DAX
  static inline vm_fault_t
  xfs_dax_fault(
@@ -1442,6 +1465,7 @@ xfs_file_mmap(
  
  const struct file_operations xfs_file_operations = {
  	.llseek		= xfs_file_llseek,
+	.llseek_nowait	= xfs_file_llseek_nowait,
  	.read_iter	= xfs_file_read_iter,
  	.write_iter	= xfs_file_write_iter,
  	.splice_read	= xfs_file_splice_read,
@@ -1467,6 +1491,7 @@ const struct file_operations xfs_dir_file_operations = {
  	.read		= generic_read_dir,
  	.iterate_shared	= xfs_file_readdir,
  	.llseek		= generic_file_llseek,
+	.llseek_nowait	= xfs_file_llseek_nowait,
  	.unlocked_ioctl	= xfs_file_ioctl,
  #ifdef CONFIG_COMPAT
  	.compat_ioctl	= xfs_file_compat_ioctl,

This is pretty nasty. It would be far better just to change the
.llseek method than to inflict this on every filesystem for the
forseeable future.

Not that I'm a fan of passing "nowait" booleans all through the file
operations methods - that way lies madness. We use a control
structure for the IO path operations (kiocb) to hold per-call
context information, perhaps we need something similar for these
other methods that people are wanting to hook up to io_uring (e.g.
readdir) so taht we don't have to play whack-a-mole with every new
io_uring method that people want and then end up with a different
nowait solution for every method.

-Dave.

whack-a-mole is exactly what I thought when I tried to find a place to
hold that...I'll think about it in next version, a generic structure for
io_uring is good I believe. I'll update this patchset after the getdents
stuff are merged.

Thanks,
Hao






