Re: [PATCH] btrfs: add io_uring interface for encoded reads

[Christoph Hellwig <hch@infradead.org>]

On Fri, Aug 09, 2024 at 06:35:27PM +0100, Mark Harmstone wrote:
> Adds an io_uring interface for asynchronous encoded reads, using the
> same interface as for the ioctl. To use this you would use an SQE opcode
> of IORING_OP_URING_CMD, the cmd_op would be BTRFS_IOC_ENCODED_READ, and
> addr would point to the userspace address of the
> btrfs_ioctl_encoded_io_args struct. As with the ioctl, you need to have
> CAP_SYS_ADMIN for this to work.

What is the point if this doesn't actually do anything but returning
-EIOCBQUEUED?

Note that that the internals of the btrfs encoded read is built
around kiocbs anyway, so you might as well turn things upside down,
implement a real async io_uring cmd and just wait for it to complete
to implement the existing synchronous ioctl.

> 
> Signed-off-by: Mark Harmstone <maharmstone@fb.com>
> ---
>  fs/btrfs/file.c  |  1 +
>  fs/btrfs/ioctl.c | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
>  fs/btrfs/ioctl.h |  1 +
>  3 files changed, 50 insertions(+)
> 
> diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
> index f9d76072398d..974f9e85b46e 100644
> --- a/fs/btrfs/file.c
> +++ b/fs/btrfs/file.c
> @@ -3850,6 +3850,7 @@ const struct file_operations btrfs_file_operations = {
>  	.compat_ioctl	= btrfs_compat_ioctl,
>  #endif
>  	.remap_file_range = btrfs_remap_file_range,
> +	.uring_cmd	= btrfs_uring_cmd,
>  };
>  
>  int btrfs_fdatawrite_range(struct inode *inode, loff_t start, loff_t end)
> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
> index 0493272a7668..8f5cc7d1429c 100644
> --- a/fs/btrfs/ioctl.c
> +++ b/fs/btrfs/ioctl.c
> @@ -29,6 +29,7 @@
>  #include <linux/fileattr.h>
>  #include <linux/fsverity.h>
>  #include <linux/sched/xacct.h>
> +#include <linux/io_uring/cmd.h>
>  #include "ctree.h"
>  #include "disk-io.h"
>  #include "export.h"
> @@ -4648,6 +4649,53 @@ static int btrfs_ioctl_encoded_write(struct file *file, void __user *argp, bool
>  	return ret;
>  }
>  
> +static void btrfs_uring_encoded_read_cb(struct io_uring_cmd *cmd,
> +					unsigned int issue_flags)
> +{
> +	int ret;
> +
> +	ret = btrfs_ioctl_encoded_read(cmd->file, (void __user *)cmd->sqe->addr,
> +				       false);
> +
> +	io_uring_cmd_done(cmd, ret, 0, issue_flags);
> +}
> +
> +static void btrfs_uring_encoded_read_compat_cb(struct io_uring_cmd *cmd,
> +					       unsigned int issue_flags)
> +{
> +	int ret;
> +
> +	ret = btrfs_ioctl_encoded_read(cmd->file, (void __user *)cmd->sqe->addr,
> +				       true);
> +
> +	io_uring_cmd_done(cmd, ret, 0, issue_flags);
> +}
> +
> +static int btrfs_uring_encoded_read(struct io_uring_cmd *cmd,
> +				    unsigned int issue_flags)
> +{
> +	if (issue_flags & IO_URING_F_COMPAT)
> +		io_uring_cmd_complete_in_task(cmd, btrfs_uring_encoded_read_compat_cb);
> +	else
> +		io_uring_cmd_complete_in_task(cmd, btrfs_uring_encoded_read_cb);
> +
> +	return -EIOCBQUEUED;
> +}
> +
> +int btrfs_uring_cmd(struct io_uring_cmd *cmd, unsigned int issue_flags)
> +{
> +	switch (cmd->cmd_op) {
> +	case BTRFS_IOC_ENCODED_READ:
> +#if defined(CONFIG_64BIT) && defined(CONFIG_COMPAT)
> +	case BTRFS_IOC_ENCODED_READ_32:
> +#endif
> +		return btrfs_uring_encoded_read(cmd, issue_flags);
> +	}
> +
> +	io_uring_cmd_done(cmd, -EINVAL, 0, issue_flags);
> +	return -EIOCBQUEUED;
> +}
> +
>  long btrfs_ioctl(struct file *file, unsigned int
>  		cmd, unsigned long arg)
>  {
> diff --git a/fs/btrfs/ioctl.h b/fs/btrfs/ioctl.h
> index 2c5dc25ec670..33578f4b5f46 100644
> --- a/fs/btrfs/ioctl.h
> +++ b/fs/btrfs/ioctl.h
> @@ -22,5 +22,6 @@ void btrfs_sync_inode_flags_to_i_flags(struct inode *inode);
>  int __pure btrfs_is_empty_uuid(u8 *uuid);
>  void btrfs_update_ioctl_balance_args(struct btrfs_fs_info *fs_info,
>  				     struct btrfs_ioctl_balance_args *bargs);
> +int btrfs_uring_cmd(struct io_uring_cmd *cmd, unsigned int issue_flags);
>  
>  #endif
> -- 
> 2.44.2
> 
> 
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