Re: [PATCH 2/2] libvhost-user: replace qemu/memfd.h usage

[Dr. David Alan Gilbert]

* marcandre.lureau@redhat.com (marcandre.lureau@redhat.com) wrote:
> From: Marc-André Lureau <marcandre.lureau@redhat.com>
> 
> Undo the damage from commit 5f9ff1eff3 ("libvhost-user: Support tracking
> inflight I/O in shared memory") which introduced glib dependency through
> osdep.h inclusion.
> 
> libvhost-user.c tries to stay free from glib usage.
> 
> Use glibc memfd_create directly when available (assumed so when
> MFD_ALLOW_SEALING is defined).
> 
> Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> ---
>  contrib/libvhost-user/libvhost-user.c | 50 +++++++++++++++++++++++----
>  1 file changed, 43 insertions(+), 7 deletions(-)
> 
> diff --git a/contrib/libvhost-user/libvhost-user.c 
> b/contrib/libvhost-user/libvhost-user.c
> index 1c1cfbf1e7..805521859d 100644
> --- a/contrib/libvhost-user/libvhost-user.c
> +++ b/contrib/libvhost-user/libvhost-user.c
> @@ -42,8 +42,6 @@
>  #endif
>  
>  #include "qemu/atomic.h"
> -#include "qemu/osdep.h"
> -#include "qemu/memfd.h"
>  
>  #include "libvhost-user.h"
>  
> @@ -1615,11 +1613,45 @@ vu_inflight_queue_size(uint16_t queue_size)
>             sizeof(uint16_t), INFLIGHT_ALIGNMENT);
>  }
>  
> +#ifdef MFD_ALLOW_SEALING
> +static void *
> +memfd_alloc(const char *name, size_t size, unsigned int flags, int *fd)
> +{
> +    void *ptr;
> +    int ret;
> +
> +    *fd = memfd_create(name, MFD_ALLOW_SEALING);
> +    if (*fd < 0) {
> +        return NULL;
> +    }
> +
> +    ret = ftruncate(*fd, size);

Do you need to do any of the page alignment?

> +    if (ret < 0) {
> +        close(*fd);
> +        return NULL;
> +    }
> +
> +    ret = fcntl(*fd, F_ADD_SEALS, F_SEAL_GROW | F_SEAL_SHRINK | F_SEAL_SEAL);

I think you'd intended to use the 'flags' parameter there.

> +    if (ret < 0) {
> +        close(*fd);
> +        return NULL;
> +    }
> +
> +    ptr = mmap(0, size, PROT_READ | PROT_WRITE, MAP_SHARED, *fd, 0);
> +    if (ptr == MAP_FAILED) {
> +        close(*fd);
> +        return NULL;
> +    }
> +
> +    return ptr;
> +}
> +#endif
> +
>  static bool
>  vu_get_inflight_fd(VuDev *dev, VhostUserMsg *vmsg)
>  {
> -    int fd;
> -    void *addr;
> +    int fd = -1;
> +    void *addr = NULL;
>      uint64_t mmap_size;
>      uint16_t num_queues, queue_size;
>  
> @@ -1637,9 +1669,13 @@ vu_get_inflight_fd(VuDev *dev, VhostUserMsg *vmsg)
>  
>      mmap_size = vu_inflight_queue_size(queue_size) * num_queues;
>  
> -    addr = qemu_memfd_alloc("vhost-inflight", mmap_size,
> -                            F_SEAL_GROW | F_SEAL_SHRINK | F_SEAL_SEAL,
> -                            &fd, NULL);
> +#ifdef MFD_ALLOW_SEALING
> +    addr = memfd_alloc("vhost-inflight", mmap_size,
> +                       F_SEAL_GROW | F_SEAL_SHRINK | F_SEAL_SEAL,
> +                       &fd);
> +#else
> +    vu_panic(dev, "Not implemented: memfd support is missing");

Should there be an ifdef somewhere on the declared features, so it
doesn't get this far because it wont negotiate the feature?

Dave

> +#endif
>  
>      if (!addr) {
>          vu_panic(dev, "Failed to alloc vhost inflight area");
> -- 
> 2.29.0
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK