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

[Chunsheng Luo]

On 1/15/26 8:23 PM, Amir Goldstein wrote:
> 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?

Yes, that's correct.

> > Signed-off-by: Chunsheng Luo <luochunsheng@xxxxxxxx>
> > ---
> >   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.
Okay, thank you for the suggestion.