On Fri, Jan 05, 2024 at 03:44:55PM -0500, Vivek Goyal wrote: > On Sat, Nov 11, 2023 at 06:53:40AM -0500, Greg KH wrote: > > On Thu, Oct 05, 2023 at 04:30:30PM -0400, Vivek Goyal wrote: > > > virtiofs filesystem is mounted using a "tag" which is exported by the > > > virtiofs device. virtiofs driver knows about all the available tags but > > > these are not exported to user space. > > > > > > People have asked these tags to be exported to user space. Most recently > > > Lennart Poettering has asked for it as he wants to scan the tags and mount > > > virtiofs automatically in certain cases. > > > > > > https://gitlab.com/virtio-fs/virtiofsd/-/issues/128 > > > > > > This patch exports tags through sysfs. One tag is associated with each > > > virtiofs device. A new "tag" file appears under virtiofs device dir. > > > Actual filesystem tag can be obtained by reading this "tag" file. > > > > > > For example, if a virtiofs device exports tag "myfs", a new file "tag" > > > will show up here. > > > > > > /sys/bus/virtio/devices/virtio<N>/tag > > > > > > # cat /sys/bus/virtio/devices/virtio<N>/tag > > > myfs > > > > > > Signed-off-by: Vivek Goyal <vgoyal@xxxxxxxxxx> > > > --- > > > fs/fuse/virtio_fs.c | 34 ++++++++++++++++++++++++++++++++++ > > > 1 file changed, 34 insertions(+) > > > > > > diff --git a/fs/fuse/virtio_fs.c b/fs/fuse/virtio_fs.c > > > index 5f1be1da92ce..a5b11e18f331 100644 > > > --- a/fs/fuse/virtio_fs.c > > > +++ b/fs/fuse/virtio_fs.c > > > @@ -107,6 +107,21 @@ static const struct fs_parameter_spec virtio_fs_parameters[] = { > > > {} > > > }; > > > > > > +/* Forward Declarations */ > > > +static void virtio_fs_stop_all_queues(struct virtio_fs *fs); > > > + > > > +/* sysfs related */ > > > +static ssize_t tag_show(struct device *dev, struct device_attribute *attr, > > > + char *buf) > > > +{ > > > + struct virtio_device *vdev = container_of(dev, struct virtio_device, > > > + dev); > > > + struct virtio_fs *fs = vdev->priv; > > > + > > > + return sysfs_emit(buf, "%s", fs->tag); > > > +} > > > +static DEVICE_ATTR_RO(tag); > > > + > > > static int virtio_fs_parse_param(struct fs_context *fsc, > > > struct fs_parameter *param) > > > { > > > @@ -265,6 +280,15 @@ static int virtio_fs_add_instance(struct virtio_fs *fs) > > > return 0; > > > } > > > > > > +static void virtio_fs_remove_instance(struct virtio_fs *fs) > > > +{ > > > + mutex_lock(&virtio_fs_mutex); > > > + list_del_init(&fs->list); > > > + virtio_fs_stop_all_queues(fs); > > > + virtio_fs_drain_all_queues_locked(fs); > > > + mutex_unlock(&virtio_fs_mutex); > > > +} > > > + > > > /* Return the virtio_fs with a given tag, or NULL */ > > > static struct virtio_fs *virtio_fs_find_instance(const char *tag) > > > { > > > @@ -891,8 +915,15 @@ static int virtio_fs_probe(struct virtio_device *vdev) > > > if (ret < 0) > > > goto out_vqs; > > > > > > + /* Export tag through sysfs */ > > > + ret = device_create_file(&vdev->dev, &dev_attr_tag); > > > + if (ret < 0) > > > + goto out_sysfs_attr; > > > > You just raced with userspace and lost :( > > > > Please use default groups for your device/bus, that is what they are > > there for. > > Hi Greg, > > Getting back to this thread after a long time. Sorry, got busy in other > things. > > Trying to understand the races with user space. IIUC, your primary concern > is that kobject has already been published to the user space and I am > trying to add/remove attributes to the object after the fact and that > makes it racy? Yes. > And suggestion is to first fully create kobject (including attrs) before > publishing it to user space. Do I understand it correctly or I missed > the point completely? Use the default groups pointer in the device instead which makes the driver core create/remove the files automatically for you. Here's something I wrote over a decade ago as to how to prevent this: http://www.kroah.com/log/blog/2013/06/26/how-to-create-a-sysfs-file-correctly/ thanks, greg k-h
