Re: [PATCH v3 06/12] vfio-user: run vfio-user context

[Stefan Hajnoczi]

On Mon, Oct 11, 2021 at 01:31:11AM -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 | 75 ++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 74 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/remote/vfio-user-obj.c b/hw/remote/vfio-user-obj.c
> index 7ce4e5b256..05f7fff19c 100644
> --- a/hw/remote/vfio-user-obj.c
> +++ b/hw/remote/vfio-user-obj.c
> @@ -42,6 +42,7 @@
>  #include "qapi/error.h"
>  #include "qapi/qapi-visit-sockets.h"
>  #include "qemu/notify.h"
> +#include "qemu/thread.h"
>  #include "sysemu/sysemu.h"
>  #include "libvfio-user.h"
>  #include "hw/qdev-core.h"
> @@ -72,6 +73,8 @@ struct VfuObject {
>      vfu_ctx_t *vfu_ctx;
>  
>      PCIDevice *pci_dev;
> +
> +    int vfu_poll_fd;
>  };
>  
>  static void vfu_object_set_socket(Object *obj, Visitor *v, const char *name,
> @@ -105,6 +108,58 @@ static void vfu_object_set_device(Object *obj, const 
> char *str, Error **errp)
>      trace_vfu_prop("device", 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->device, strerror(errno));
> +                 break;
> +            }

The libvfio-user.h doc comments say this function can return -1 (EAGAIN)
when LIBVFIO_USER_FLAG_ATTACH_NB was used. Is the doc comment wrong
since this patch seems to rely on vfu_run_ctx() returning 0 when there
are no more commands to process?

> +        }
> +    }
> +}
> +
> +static void vfu_object_attach_ctx(void *opaque)
> +{
> +    VfuObject *o = opaque;
> +    int ret;
> +
> +    qemu_set_fd_handler(o->vfu_poll_fd, NULL, NULL, NULL);
> +    o->vfu_poll_fd = -1;
> +
> +retry_attach:
> +    ret = vfu_attach_ctx(o->vfu_ctx);
> +    if (ret < 0 && (errno == EAGAIN || errno == EWOULDBLOCK)) {
> +        goto retry_attach;

Can we wait for the poll fd to become readable instead of spinning? I
don't know the libvfio-user APIs so I'm not sure, but it would be nice
to avoid a busy loop.

> +    } else if (ret < 0) {
> +        error_setg(&error_abort,

error_abort is not appropriate for hotplugged objects, where it's less
likely that the user wants to terminate the process when a failure
occurs. If asynchronous errors occur then QMP Events should be raised so
the QMP client gets notified and can deal with them.

> +                   "vfu: Failed to attach device %s to context - %s",
> +                   o->device, strerror(errno));
> +        return;
> +    }
> +
> +    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->device);
> +        return;
> +    }
> +
> +    qemu_set_fd_handler(o->vfu_poll_fd, vfu_object_ctx_run, NULL, o);
> +}
> +
>  /*
>   * vfio-user-server depends on the availability of the 'socket' and 'device'
>   * properties. It also depends on devices instantiated in QEMU. These
> @@ -120,7 +175,8 @@ static void vfu_object_machine_done(Notifier *notifier, 
> void *data)
>      vfu_pci_type_t pci_type = VFU_PCI_TYPE_CONVENTIONAL;
>      int ret;
>  
> -    o->vfu_ctx = vfu_create_ctx(VFU_TRANS_SOCK, o->socket->u.q_unix.path, 0,
> +    o->vfu_ctx = vfu_create_ctx(VFU_TRANS_SOCK, o->socket->u.q_unix.path,
> +                                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",
> @@ -152,6 +208,21 @@ static void vfu_object_machine_done(Notifier *notifier, 
> void *data)
>                     o->device, 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->device, strerror(errno));
> +        return;
> +    }
> +
> +    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->device);
> +        return;
> +    }
> +
> +    qemu_set_fd_handler(o->vfu_poll_fd, vfu_object_attach_ctx, NULL, o);
>  }
>  
>  static void vfu_object_init(Object *obj)
> @@ -178,6 +249,8 @@ 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;

This must be done before the qemu_add_machine_init_done_notifier() call
in the hotplug case. qemu_add_machine_init_done_notifier() invokes the
notifier callback immediately if machine init was already done.

signature.asc
Description: PGP signature