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Correctly-formatted patch follows. Should I send out a > V2 instead? > > Add support for opening and closing backing files in the fuse_uring_cmd > callback. Store backing_map (for open) and backing_id (for close) in the > uring_cmd data. > --- > fs/fuse/dev_uring.c | 50 +++++++++++++++++++++++++++++++++++++++ > include/uapi/linux/fuse.h | 6 +++++ > 2 files changed, 56 insertions(+) > > diff --git a/fs/fuse/dev_uring.c b/fs/fuse/dev_uring.c > index ebd2931b4f2a..df73d9d7e686 100644 > --- a/fs/fuse/dev_uring.c > +++ b/fs/fuse/dev_uring.c > @@ -1033,6 +1033,40 @@ fuse_uring_create_ring_ent(struct io_uring_cmd *cm= d, > return ent; > } > > +/* > + * Register new backing file for passthrough, getting backing map from > URING_CMD data > + */ > +static int fuse_uring_backing_open(struct io_uring_cmd *cmd, > + unsigned int issue_flags, struct fuse_conn *fc) > +{ > + const struct fuse_backing_map *map =3D io_uring_sqe_cmd(cmd->sqe); > + int ret =3D fuse_backing_open(fc, map); > + I am not that familiar with io_uring, so I need to ask - fuse_backing_open() does fb->cred =3D prepare_creds(); to record server credentials what are the credentials that will be recorded in the context of this io_uring command? > + if (ret < 0) { > + return ret; > + } > + > + io_uring_cmd_done(cmd, ret, 0, issue_flags); > + return 0; > +} > + > +/* > + * Remove file from passthrough tracking, getting backing_id from > URING_CMD data > + */ > +static int fuse_uring_backing_close(struct io_uring_cmd *cmd, > + unsigned int issue_flags, struct fuse_conn *fc) > +{ > + const int *backing_id =3D io_uring_sqe_cmd(cmd->sqe); > + int ret =3D fuse_backing_close(fc, *backing_id); > + > + if (ret < 0) { > + return ret; > + } > + > + io_uring_cmd_done(cmd, ret, 0, issue_flags); > + return 0; > +} > + > /* > * Register header and payload buffer with the kernel and puts the > * entry as "ready to get fuse requests" on the queue > @@ -1144,6 +1178,22 @@ int fuse_uring_cmd(struct io_uring_cmd *cmd, > unsigned int issue_flags) > return err; > } > break; > + case FUSE_IO_URING_CMD_BACKING_OPEN: > + err =3D fuse_uring_backing_open(cmd, issue_flags, fc); > + if (err) { > + pr_info_once("FUSE_IO_URING_CMD_BACKING_OPEN failed err=3D%d= \n", > + err); > + return err; > + } > + break; > + case FUSE_IO_URING_CMD_BACKING_CLOSE: > + err =3D fuse_uring_backing_close(cmd, issue_flags, fc); > + if (err) { > + pr_info_once("FUSE_IO_URING_CMD_BACKING_CLOSE failed err=3D%= d\n", > + err); > + return err; > + } > + break; > default: > return -EINVAL; > } > diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h > index 5e0eb41d967e..634265da1328 100644 > --- a/include/uapi/linux/fuse.h > +++ b/include/uapi/linux/fuse.h > @@ -1264,6 +1264,12 @@ enum fuse_uring_cmd { > > /* commit fuse request result and fetch next request */ > FUSE_IO_URING_CMD_COMMIT_AND_FETCH =3D 2, > + > + /* add new backing file for passthrough */ > + FUSE_IO_URING_CMD_BACKING_OPEN =3D 3, > + > + /* remove passthrough file by backing_id */ > + FUSE_IO_URING_CMD_BACKING_CLOSE =3D 4, > }; > An anecdote: Why are we using FUSE_DEV_IOC_BACKING_OPEN and not passing the backing fd directly in OPEN response? The reason for that was security related - there was a concern that an adversary would be able to trick some process into writing some fd to /dev/fuse, whereas tricking some proces into doing an ioctl is not so realistic. AFAICT this concern does not exist when OPEN response is via io_uring(?), so the backing_id indirection is not strictly needed, but for the sake of uniformity with standard fuse protocol, I guess we should maintain those commands in io_uring as well. Thanks, Amir.