| Message ID | 20240208193212.731978-4-stefanha@redhat.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | virtiofs: export filesystem tags through sysfs | expand |
On Thu, Feb 08, 2024 at 02:32:11PM -0500, Stefan Hajnoczi wrote: > Alyssa Ross <hi@alyssa.is> requested that virtiofs notifies userspace > when filesytems become available. This can be used to detect when a > filesystem with a given tag is hotplugged, for example. uevents allow > userspace to detect changes without resorting to polling. > > The tag is included as a uevent property so it's easy for userspace to > identify the filesystem in question even when the sysfs directory goes > away during removal. > > Here are example uevents: > > # udevadm monitor -k -p > > KERNEL[111.113221] add /fs/virtiofs/2 (virtiofs) > ACTION=add > DEVPATH=/fs/virtiofs/2 > SUBSYSTEM=virtiofs > TAG=test > > KERNEL[165.527167] remove /fs/virtiofs/2 (virtiofs) > ACTION=remove > DEVPATH=/fs/virtiofs/2 > SUBSYSTEM=virtiofs > TAG=test > > Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> > --- > fs/fuse/virtio_fs.c | 15 +++++++++++++++ > 1 file changed, 15 insertions(+) > > diff --git a/fs/fuse/virtio_fs.c b/fs/fuse/virtio_fs.c > index 28e96b7cde00..18a8f531e5d4 100644 > --- a/fs/fuse/virtio_fs.c > +++ b/fs/fuse/virtio_fs.c > @@ -270,6 +270,17 @@ static void virtio_fs_start_all_queues(struct virtio_fs *fs) > } > } > > +static void virtio_fs_uevent(struct virtio_fs *fs, enum kobject_action action) > +{ > + char tag_str[sizeof("TAG=") + > + sizeof_field(struct virtio_fs_config, tag) + 1]; > + char *envp[] = {tag_str, NULL}; > + > + snprintf(tag_str, sizeof(tag_str), "TAG=%s", fs->tag); > + > + kobject_uevent_env(&fs->kobj, action, envp); > +} > + > /* Add a new instance to the list or return -EEXIST if tag name exists*/ > static int virtio_fs_add_instance(struct virtio_device *vdev, > struct virtio_fs *fs) > @@ -309,6 +320,8 @@ static int virtio_fs_add_instance(struct virtio_device *vdev, > > mutex_unlock(&virtio_fs_mutex); > > + virtio_fs_uevent(fs, KOBJ_ADD); Why do you have to explicitly ask for the event? Doesn't sysfs trigger this for you automatically? Set the kset uevent callback for this, right? thanks, greg k-h
On Fri, Feb 09, 2024 at 10:39:04AM +0000, Greg KH wrote: > On Thu, Feb 08, 2024 at 02:32:11PM -0500, Stefan Hajnoczi wrote: > > Alyssa Ross <hi@alyssa.is> requested that virtiofs notifies userspace > > when filesytems become available. This can be used to detect when a > > filesystem with a given tag is hotplugged, for example. uevents allow > > userspace to detect changes without resorting to polling. > > > > The tag is included as a uevent property so it's easy for userspace to > > identify the filesystem in question even when the sysfs directory goes > > away during removal. > > > > Here are example uevents: > > > > # udevadm monitor -k -p > > > > KERNEL[111.113221] add /fs/virtiofs/2 (virtiofs) > > ACTION=add > > DEVPATH=/fs/virtiofs/2 > > SUBSYSTEM=virtiofs > > TAG=test > > > > KERNEL[165.527167] remove /fs/virtiofs/2 (virtiofs) > > ACTION=remove > > DEVPATH=/fs/virtiofs/2 > > SUBSYSTEM=virtiofs > > TAG=test > > > > Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> > > --- > > fs/fuse/virtio_fs.c | 15 +++++++++++++++ > > 1 file changed, 15 insertions(+) > > > > diff --git a/fs/fuse/virtio_fs.c b/fs/fuse/virtio_fs.c > > index 28e96b7cde00..18a8f531e5d4 100644 > > --- a/fs/fuse/virtio_fs.c > > +++ b/fs/fuse/virtio_fs.c > > @@ -270,6 +270,17 @@ static void virtio_fs_start_all_queues(struct virtio_fs *fs) > > } > > } > > > > +static void virtio_fs_uevent(struct virtio_fs *fs, enum kobject_action action) > > +{ > > + char tag_str[sizeof("TAG=") + > > + sizeof_field(struct virtio_fs_config, tag) + 1]; > > + char *envp[] = {tag_str, NULL}; > > + > > + snprintf(tag_str, sizeof(tag_str), "TAG=%s", fs->tag); > > + > > + kobject_uevent_env(&fs->kobj, action, envp); > > +} > > + > > /* Add a new instance to the list or return -EEXIST if tag name exists*/ > > static int virtio_fs_add_instance(struct virtio_device *vdev, > > struct virtio_fs *fs) > > @@ -309,6 +320,8 @@ static int virtio_fs_add_instance(struct virtio_device *vdev, > > > > mutex_unlock(&virtio_fs_mutex); > > > > + virtio_fs_uevent(fs, KOBJ_ADD); > > Why do you have to explicitly ask for the event? Doesn't sysfs trigger > this for you automatically? Set the kset uevent callback for this, > right? I haven't found a way to get an implicit KOBJ_ADD uevent. device_add() and other kset_uevent_ops users emit KOBJ_ADD manually too. Grepping for KOBJ_ADD in fs/sysfs/ and lib/ doesn't produce any useful results either. It is possible to eliminate the explicit KOBJ_REMOVE though because kobject_del() already calls it. I will fix that and switch to kset_uevent_ops->uevent(). Thanks, Stefan
diff --git a/fs/fuse/virtio_fs.c b/fs/fuse/virtio_fs.c index 28e96b7cde00..18a8f531e5d4 100644 --- a/fs/fuse/virtio_fs.c +++ b/fs/fuse/virtio_fs.c @@ -270,6 +270,17 @@ static void virtio_fs_start_all_queues(struct virtio_fs *fs) } } +static void virtio_fs_uevent(struct virtio_fs *fs, enum kobject_action action) +{ + char tag_str[sizeof("TAG=") + + sizeof_field(struct virtio_fs_config, tag) + 1]; + char *envp[] = {tag_str, NULL}; + + snprintf(tag_str, sizeof(tag_str), "TAG=%s", fs->tag); + + kobject_uevent_env(&fs->kobj, action, envp); +} + /* Add a new instance to the list or return -EEXIST if tag name exists*/ static int virtio_fs_add_instance(struct virtio_device *vdev, struct virtio_fs *fs) @@ -309,6 +320,8 @@ static int virtio_fs_add_instance(struct virtio_device *vdev, mutex_unlock(&virtio_fs_mutex); + virtio_fs_uevent(fs, KOBJ_ADD); + return 0; } @@ -977,6 +990,8 @@ static void virtio_fs_remove(struct virtio_device *vdev) { struct virtio_fs *fs = vdev->priv; + virtio_fs_uevent(fs, KOBJ_REMOVE); + mutex_lock(&virtio_fs_mutex); /* This device is going away. No one should get new reference */ list_del_init(&fs->list);
Alyssa Ross <hi@alyssa.is> requested that virtiofs notifies userspace when filesytems become available. This can be used to detect when a filesystem with a given tag is hotplugged, for example. uevents allow userspace to detect changes without resorting to polling. The tag is included as a uevent property so it's easy for userspace to identify the filesystem in question even when the sysfs directory goes away during removal. Here are example uevents: # udevadm monitor -k -p KERNEL[111.113221] add /fs/virtiofs/2 (virtiofs) ACTION=add DEVPATH=/fs/virtiofs/2 SUBSYSTEM=virtiofs TAG=test KERNEL[165.527167] remove /fs/virtiofs/2 (virtiofs) ACTION=remove DEVPATH=/fs/virtiofs/2 SUBSYSTEM=virtiofs TAG=test Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> --- fs/fuse/virtio_fs.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+)