Re: [RFC 1/2] fuse: add close all in passthrough backing close for crash recovery

[Amir Goldstein <amir73il@gmail.com>]

On Thu, Jan 15, 2026 at 03:20:30PM +0800, Chunsheng Luo wrote:
> Simplify FUSE daemon crash recovery by avoiding persistence of
> backing_ids, thereby improving availability and reducing performance
> overhead.
> 
> Non-persistent backing_ids after crash recovery may lead to resource
> leaks if backing file resources are not properly cleaned up during
> daemon restart.
> 
> Add a close_all handler to the backing close operation. This ensures
> comprehensive cleanup of all backing file resources when the FUSE
> daemon restarts, preventing resource leaks while maintaining the
> simplified recovery approach.

Am I correct to assume that you are referring to FUSE server restart
where the /dev/fuse fd is stored in an external fd store and reused by
the new FUSE server instance?

> 
> Signed-off-by: Chunsheng Luo <luochunsheng@ustc.edu>
> ---
>  fs/fuse/backing.c | 14 ++++++++++++++
>  fs/fuse/dev.c     |  5 +++++
>  fs/fuse/fuse_i.h  |  1 +
>  3 files changed, 20 insertions(+)
> 
> diff --git a/fs/fuse/backing.c b/fs/fuse/backing.c
> index 4afda419dd14..34d0ea62fb9b 100644
> --- a/fs/fuse/backing.c
> +++ b/fs/fuse/backing.c
> @@ -166,6 +166,20 @@ int fuse_backing_close(struct fuse_conn *fc, int backing_id)
>  	return err;
>  }
>  
> +static int fuse_backing_close_one(int id, void *p, void *data)
> +{
> +	struct fuse_conn *fc = data;
> +
> +	fuse_backing_close(fc, id);
> +
> +	return 0;
> +}
> +
> +void fuse_backing_close_all(struct fuse_conn *fc)
> +{
> +	idr_for_each(&fc->backing_files_map, fuse_backing_close_one, fc);
> +}
> +
>  struct fuse_backing *fuse_backing_lookup(struct fuse_conn *fc, int backing_id)
>  {
>  	struct fuse_backing *fb;
> diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
> index 6d59cbc877c6..25f6bb58623d 100644
> --- a/fs/fuse/dev.c
> +++ b/fs/fuse/dev.c
> @@ -2651,6 +2651,11 @@ static long fuse_dev_ioctl_backing_close(struct file *file, __u32 __user *argp)
>  	if (get_user(backing_id, argp))
>  		return -EFAULT;
>  
> +	if (backing_id == -1) {
> +		fuse_backing_close_all(fud->fc);
> +		return 0;
> +	}
> +

I think that an explicit new ioctl FUSE_DEV_IOC_BACKING_CLOSE_ALL
is called for this very intrusive operation.

Sending FUSE_DEV_IOC_BACKING_CLOSE with backing_id -1 could
just as well happen by mistake.

Thanks,
Amir.