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

[Chunsheng Luo <luochunsheng@ustc.edu>]

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@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.
> 
> 
Okay, thank you for the suggestion.