Re: [PATCH 1/2] fuse: fix COPY_FILE_RANGE interface

[Luis Henriques <luis@igalia.com>]

On Tue, Aug 05 2025, Miklos Szeredi wrote:

> The FUSE protocol uses struct fuse_write_out to convey the return value of
> copy_file_range, which is restricted to uint32_t.  But the COPY_FILE_RANGE
> interface supports a 64-bit size copies.
>
> Currently the number of bytes copied is silently truncated to 32-bit, which
> is unfortunate at best.
>
> Introduce a new op COPY_FILE_RANGE_64, which is identical, except the
> number of bytes copied is returned in a 64-bit value.
>
> If the fuse server does not support COPY_FILE_RANGE_64, fall back to
> COPY_FILE_RANGE and truncate the size to UINT_MAX - 4096.

I was wondering if it wouldn't make more sense to truncate the size to
MAX_RW_COUNT instead.  My reasoning is that, if I understand the code
correctly (which is probably a big 'if'!), the VFS will fallback to
splice() if the file system does not implement copy_file_range.  And in
this case splice() seems to limit the operation to MAX_RW_COUNT.

Cheers,
-- 
Luís


> Reported-by: Florian Weimer <fweimer@redhat.com>
> Closes: https://lore.kernel.org/all/lhuh5ynl8z5.fsf@oldenburg.str.redhat.com/
> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
> ---
>  fs/fuse/file.c            | 34 ++++++++++++++++++++++++++--------
>  fs/fuse/fuse_i.h          |  3 +++
>  include/uapi/linux/fuse.h | 12 +++++++++++-
>  3 files changed, 40 insertions(+), 9 deletions(-)
>
> diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> index adc4aa6810f5..bd6624885855 100644
> --- a/fs/fuse/file.c
> +++ b/fs/fuse/file.c
> @@ -3017,6 +3017,8 @@ static ssize_t __fuse_copy_file_range(struct file *file_in, loff_t pos_in,
>  		.flags = flags
>  	};
>  	struct fuse_write_out outarg;
> +	struct fuse_copy_file_range_out outarg_64;
> +	u64 bytes_copied;
>  	ssize_t err;
>  	/* mark unstable when write-back is not used, and file_out gets
>  	 * extended */
> @@ -3066,30 +3068,46 @@ static ssize_t __fuse_copy_file_range(struct file *file_in, loff_t pos_in,
>  	if (is_unstable)
>  		set_bit(FUSE_I_SIZE_UNSTABLE, &fi_out->state);
>  
> -	args.opcode = FUSE_COPY_FILE_RANGE;
> +	args.opcode = FUSE_COPY_FILE_RANGE_64;
>  	args.nodeid = ff_in->nodeid;
>  	args.in_numargs = 1;
>  	args.in_args[0].size = sizeof(inarg);
>  	args.in_args[0].value = &inarg;
>  	args.out_numargs = 1;
> -	args.out_args[0].size = sizeof(outarg);
> -	args.out_args[0].value = &outarg;
> +	args.out_args[0].size = sizeof(outarg_64);
> +	args.out_args[0].value = &outarg_64;
> +	if (fc->no_copy_file_range_64) {
> +fallback:
> +		/* Fall back to old op that can't handle large copy length */
> +		args.opcode = FUSE_COPY_FILE_RANGE;
> +		args.out_args[0].size = sizeof(outarg);
> +		args.out_args[0].value = &outarg;
> +		inarg.len = min_t(size_t, len, 0xfffff000);
> +	}
>  	err = fuse_simple_request(fm, &args);
>  	if (err == -ENOSYS) {
> -		fc->no_copy_file_range = 1;
> -		err = -EOPNOTSUPP;
> +		if (fc->no_copy_file_range_64) {
> +			fc->no_copy_file_range = 1;
> +			err = -EOPNOTSUPP;
> +		} else {
> +			fc->no_copy_file_range_64 = 1;
> +			goto fallback;
> +		}
>  	}
>  	if (err)
>  		goto out;
>  
> +	bytes_copied = fc->no_copy_file_range_64 ?
> +		outarg.size : outarg_64.bytes_copied;
> +
>  	truncate_inode_pages_range(inode_out->i_mapping,
>  				   ALIGN_DOWN(pos_out, PAGE_SIZE),
> -				   ALIGN(pos_out + outarg.size, PAGE_SIZE) - 1);
> +				   ALIGN(pos_out + bytes_copied, PAGE_SIZE) - 1);
>  
>  	file_update_time(file_out);
> -	fuse_write_update_attr(inode_out, pos_out + outarg.size, outarg.size);
> +	fuse_write_update_attr(inode_out, pos_out + bytes_copied, bytes_copied);
>  
> -	err = outarg.size;
> +	err = bytes_copied;
>  out:
>  	if (is_unstable)
>  		clear_bit(FUSE_I_SIZE_UNSTABLE, &fi_out->state);
> diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
> index b54f4f57789f..a8be19f686b1 100644
> --- a/fs/fuse/fuse_i.h
> +++ b/fs/fuse/fuse_i.h
> @@ -850,6 +850,9 @@ struct fuse_conn {
>  	/** Does the filesystem support copy_file_range? */
>  	unsigned no_copy_file_range:1;
>  
> +	/** Does the filesystem support copy_file_range_64? */
> +	unsigned no_copy_file_range_64:1;
> +
>  	/* Send DESTROY request */
>  	unsigned int destroy:1;
>  
> diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
> index 122d6586e8d4..94621f68a5cc 100644
> --- a/include/uapi/linux/fuse.h
> +++ b/include/uapi/linux/fuse.h
> @@ -235,6 +235,10 @@
>   *
>   *  7.44
>   *  - add FUSE_NOTIFY_INC_EPOCH
> + *
> + *  7.45
> + *  - add FUSE_COPY_FILE_RANGE_64
> + *  - add struct fuse_copy_file_range_out
>   */
>  
>  #ifndef _LINUX_FUSE_H
> @@ -270,7 +274,7 @@
>  #define FUSE_KERNEL_VERSION 7
>  
>  /** Minor version number of this interface */
> -#define FUSE_KERNEL_MINOR_VERSION 44
> +#define FUSE_KERNEL_MINOR_VERSION 45
>  
>  /** The node ID of the root inode */
>  #define FUSE_ROOT_ID 1
> @@ -657,6 +661,7 @@ enum fuse_opcode {
>  	FUSE_SYNCFS		= 50,
>  	FUSE_TMPFILE		= 51,
>  	FUSE_STATX		= 52,
> +	FUSE_COPY_FILE_RANGE_64	= 53,
>  
>  	/* CUSE specific operations */
>  	CUSE_INIT		= 4096,
> @@ -1148,6 +1153,11 @@ struct fuse_copy_file_range_in {
>  	uint64_t	flags;
>  };
>  
> +/* For FUSE_COPY_FILE_RANGE_64 */
> +struct fuse_copy_file_range_out {
> +	uint64_t	bytes_copied;
> +};
> +
>  #define FUSE_SETUPMAPPING_FLAG_WRITE (1ull << 0)
>  #define FUSE_SETUPMAPPING_FLAG_READ (1ull << 1)
>  struct fuse_setupmapping_in {
> -- 
> 2.49.0
>