On Thu, Sep 30, 2021 at 10:38:42AM -0400, Vivek Goyal wrote: > Hi, > > As of now we do not support blocking remote posix locks with virtiofs. > Well fuse client does not care but server returns -EOPNOTSUPP. Posted corresponding qemu/virtiofsd changes here. https://listman.redhat.com/archives/virtio-fs/2021-September/msg00153.html Thanks Vivek > > There are couple of reasons to not support it yet. > > - If virtiofsd is single threaded or does not have a thread pool just > to handle requests which can block for a long time, virtiofsd will > stop processing new requests and virtiofs will come to a halt. > To the extent that further unlock request will not make progress > and deadlock will result. This can be taken care of by creating > a custom thread pool in virtiofsd just to hanlde lock requests. > > - If client sends a blocking lock request and blocks, then it will > consume descriptors in vring. If enough processes block, it is > possible that vring does not have capacity to send more requests > till some response comes back and descriptors are free. This can > also lead to deadlock where an unlock request can't be sent to > virtiofsd now. Also this will stop virtiofs operation as well as > new filesystem requests can't be sent. > > To avoid this issue, idea was suggested thatn when a blocking > lock request is sent by client, do not block it. Immediately > send a reply saying client process should wait for a notification > which will let it know once lock is available. This will make > sure descriptors in virtqueue are not kept busy while we are > waiting for lock and future unlock and other file system requests > can continue to make progress. > > This first requires a notion of notification queue and virtiosfd > being able to send notifications to client. This patch series > implements that as well. > > As of now only one notification type has been implemented but now > infrastructure is in place and other use cases should be easily > add more type of notifications as need be. > > We don't yet have the capability to interrupt the process which > is waiting for the posix lock. And reason for that is that virtiofs > does not support capability to interrupt yet. That's a TODO item > for later. > > Please have a look. > > Thanks > Vivek > > Vivek Goyal (8): > virtiofs: Disable interrupt requests properly > virtiofs: Fix a comment about fuse_dev allocation > virtiofs: Add an index to keep track of first request queue > virtiofs: Decouple queue index and queue type > virtiofs: Add a virtqueue for notifications > virtiofs: Add a helper to end request and decrement inflight number > virtiofs: Add new notification type FUSE_NOTIFY_LOCK > virtiofs: Handle reordering of reply and notification event > > fs/fuse/virtio_fs.c | 438 ++++++++++++++++++++++++++++++--- > include/uapi/linux/fuse.h | 11 +- > include/uapi/linux/virtio_fs.h | 5 + > 3 files changed, 412 insertions(+), 42 deletions(-) > > -- > 2.31.1 >
