Re: [Qemu-devel] [PATCH for-2.12] memfd: fix vhost-user-test on non-memfd capable host

[Paolo Bonzini <pbonzini@redhat.com>]

On 28/03/2018 14:18, Marc-André Lureau wrote:
> On RHEL7, memfd is not supported, and vhost-user-test fails:
> TEST: tests/vhost-user-test... (pid=10248)
>   /x86_64/vhost-user/migrate:
>   qemu-system-x86_64: -object memory-backend-memfd,id=mem,size=2M,: failed to create memfd
> FAIL
> 
> There is a qemu_memfd_check() to prevent running memfd path, but it
> also checks for fallback implementation. Let's specialize
> qemu_memfd_check() to check memfd only, while qemu_memfd_alloc_check()
> checks for the qemu_memfd_alloc() API.
> 
> Reported-by: Miroslav Rezanina <mrezanin@redhat.com>
> Tested-by: Miroslav Rezanina <mrezanin@redhat.com>
> Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> ---
>  include/qemu/memfd.h |  1 +
>  hw/virtio/vhost.c    |  2 +-
>  util/memfd.c         | 30 +++++++++++++++++++++++++++++-
>  3 files changed, 31 insertions(+), 2 deletions(-)
> 
> diff --git a/include/qemu/memfd.h b/include/qemu/memfd.h
> index de10198ed6..49e79634da 100644
> --- a/include/qemu/memfd.h
> +++ b/include/qemu/memfd.h
> @@ -18,6 +18,7 @@
>  
>  int qemu_memfd_create(const char *name, size_t size, bool hugetlb,
>                        uint64_t hugetlbsize, unsigned int seals, Error **errp);
> +bool qemu_memfd_alloc_check(void);
>  void *qemu_memfd_alloc(const char *name, size_t size, unsigned int seals,
>                         int *fd, Error **errp);
>  void qemu_memfd_free(void *ptr, size_t size, int fd);
> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> index 250f886acb..27c1ec5fe8 100644
> --- a/hw/virtio/vhost.c
> +++ b/hw/virtio/vhost.c
> @@ -1223,7 +1223,7 @@ int vhost_dev_init(struct vhost_dev *hdev, void *opaque,
>          if (!(hdev->features & (0x1ULL << VHOST_F_LOG_ALL))) {
>              error_setg(&hdev->migration_blocker,
>                         "Migration disabled: vhost lacks VHOST_F_LOG_ALL feature.");
> -        } else if (vhost_dev_log_is_shared(hdev) && !qemu_memfd_check()) {
> +        } else if (vhost_dev_log_is_shared(hdev) && !qemu_memfd_alloc_check()) {
>              error_setg(&hdev->migration_blocker,
>                         "Migration disabled: failed to allocate shared memory");
>          }
> diff --git a/util/memfd.c b/util/memfd.c
> index 07d579ea7d..277f7211af 100644
> --- a/util/memfd.c
> +++ b/util/memfd.c
> @@ -173,7 +173,13 @@ enum {
>      MEMFD_TODO
>  };
>  
> -bool qemu_memfd_check(void)
> +/**
> + * qemu_memfd_alloc_check():
> + *
> + * Check if qemu_memfd_alloc() can allocate, including using a
> + * fallback implementation when host doesn't support memfd.
> + */
> +bool qemu_memfd_alloc_check(void)
>  {
>      static int memfd_check = MEMFD_TODO;
>  
> @@ -188,3 +194,25 @@ bool qemu_memfd_check(void)
>  
>      return memfd_check == MEMFD_OK;
>  }
> +
> +/**
> + * qemu_memfd_check():
> + *
> + * Check if host supports memfd.
> + */
> +bool qemu_memfd_check(void)
> +{
> +    static int memfd_check = MEMFD_TODO;
> +
> +    if (memfd_check == MEMFD_TODO) {
> +        int mfd = memfd_create("test", 0);
> +        if (mfd >= 0) {
> +            memfd_check = MEMFD_OK;
> +            close(mfd);
> +        } else {
> +            memfd_check = MEMFD_KO;
> +        }
> +    }
> +
> +    return memfd_check == MEMFD_OK;
> +}
> 

Queued, thanks.

Paolo