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Re: [PATCH RFC server v2 05/11] vfio-user: run vfio-user context
From: |
Stefan Hajnoczi |
Subject: |
Re: [PATCH RFC server v2 05/11] vfio-user: run vfio-user context |
Date: |
Wed, 8 Sep 2021 13:58:46 +0100 |
On Fri, Aug 27, 2021 at 01:53:24PM -0400, Jagannathan Raman wrote:
> Setup a handler to run vfio-user context. The context is driven by
> messages to the file descriptor associated with it - get the fd for
> the context and hook up the handler with it
>
> Signed-off-by: Elena Ufimtseva <elena.ufimtseva@oracle.com>
> Signed-off-by: John G Johnson <john.g.johnson@oracle.com>
> Signed-off-by: Jagannathan Raman <jag.raman@oracle.com>
> ---
> hw/remote/vfio-user-obj.c | 71
> ++++++++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 70 insertions(+), 1 deletion(-)
>
> diff --git a/hw/remote/vfio-user-obj.c b/hw/remote/vfio-user-obj.c
> index 5ae0991..0726eb9 100644
> --- a/hw/remote/vfio-user-obj.c
> +++ b/hw/remote/vfio-user-obj.c
> @@ -35,6 +35,7 @@
> #include "trace.h"
> #include "sysemu/runstate.h"
> #include "qemu/notify.h"
> +#include "qemu/thread.h"
> #include "qapi/error.h"
> #include "sysemu/sysemu.h"
> #include "libvfio-user.h"
> @@ -65,6 +66,8 @@ struct VfuObject {
> vfu_ctx_t *vfu_ctx;
>
> PCIDevice *pci_dev;
> +
> + int vfu_poll_fd;
> };
>
> static void vfu_object_set_socket(Object *obj, const char *str, Error **errp)
> @@ -89,13 +92,67 @@ static void vfu_object_set_devid(Object *obj, const char
> *str, Error **errp)
> trace_vfu_prop("devid", str);
> }
>
> +static void vfu_object_ctx_run(void *opaque)
> +{
> + VfuObject *o = opaque;
> + int ret = -1;
> +
> + while (ret != 0) {
> + ret = vfu_run_ctx(o->vfu_ctx);
> + if (ret < 0) {
> + if (errno == EINTR) {
> + continue;
> + } else if (errno == ENOTCONN) {
> + qemu_set_fd_handler(o->vfu_poll_fd, NULL, NULL, NULL);
> + o->vfu_poll_fd = -1;
> + object_unparent(OBJECT(o));
> + break;
> + } else {
> + error_setg(&error_abort, "vfu: Failed to run device %s - %s",
> + o->devid, strerror(errno));
> + break;
> + }
> + }
> + }
> +}
> +
> +static void *vfu_object_attach_ctx(void *opaque)
> +{
> + VfuObject *o = opaque;
> + int ret;
> +
> +retry_attach:
> + ret = vfu_attach_ctx(o->vfu_ctx);
> + if (ret < 0 && (errno == EAGAIN || errno == EWOULDBLOCK)) {
Does this loop consume 100% CPU since this is non-blocking?
Is it possible to register the fd with a QEMU AioContext instead of
spawning a separate thread?
libvfio-user has non-blocking listen_fd but conn_fd is always blocking.
This means ATTACH_NB is not useful because vfu_attach_ctx() is actually
blocking. I think this means vfu_run_ctx() is also blocking in some
places and QEMU's event loop might hang :(.
Can you make libvfio-user non-blocking in order to solve these issues?
> + goto retry_attach;
> + } else if (ret < 0) {
> + error_setg(&error_abort,
> + "vfu: Failed to attach device %s to context - %s",
> + o->devid, strerror(errno));
> + return NULL;
> + }
> +
> + o->vfu_poll_fd = vfu_get_poll_fd(o->vfu_ctx);
> + if (o->vfu_poll_fd < 0) {
> + error_setg(&error_abort, "vfu: Failed to get poll fd %s", o->devid);
> + return NULL;
> + }
> +
> + qemu_set_fd_handler(o->vfu_poll_fd, vfu_object_ctx_run,
> + NULL, o);
> +
> + return NULL;
> +}
> +
> static void vfu_object_machine_done(Notifier *notifier, void *data)
> {
> VfuObject *o = container_of(notifier, VfuObject, machine_done);
> DeviceState *dev = NULL;
> + QemuThread thread;
> int ret;
>
> - o->vfu_ctx = vfu_create_ctx(VFU_TRANS_SOCK, o->socket, 0,
> + o->vfu_ctx = vfu_create_ctx(VFU_TRANS_SOCK, o->socket,
> + LIBVFIO_USER_FLAG_ATTACH_NB,
> o, VFU_DEV_TYPE_PCI);
> if (o->vfu_ctx == NULL) {
> error_setg(&error_abort, "vfu: Failed to create context - %s",
> @@ -124,6 +181,16 @@ static void vfu_object_machine_done(Notifier *notifier,
> void *data)
> o->devid, strerror(errno));
> return;
> }
> +
> + ret = vfu_realize_ctx(o->vfu_ctx);
> + if (ret < 0) {
> + error_setg(&error_abort, "vfu: Failed to realize device %s- %s",
> + o->devid, strerror(errno));
> + return;
> + }
> +
> + qemu_thread_create(&thread, o->socket, vfu_object_attach_ctx, o,
> + QEMU_THREAD_DETACHED);
Is this thread leaked when the object is destroyed?
> }
>
> static void vfu_object_init(Object *obj)
> @@ -147,6 +214,8 @@ static void vfu_object_init(Object *obj)
>
> o->machine_done.notify = vfu_object_machine_done;
> qemu_add_machine_init_done_notifier(&o->machine_done);
> +
> + o->vfu_poll_fd = -1;
> }
>
> static void vfu_object_finalize(Object *obj)
> --
> 1.8.3.1
>
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