Re: [Qemu-devel] [PATCH v5 1/6] memfd: split qemu_memfd_alloc()

[Philippe Mathieu-Daudé]

On 10/23/2017 06:59 AM, Marc-André Lureau wrote:
> Add a function to only create a memfd, without mmap. The function is
> used in the following memory backend.
> 
> Signed-off-by: Marc-André Lureau <address@hidden>
> ---
>  include/qemu/memfd.h |  1 +
>  util/memfd.c         | 61 
> +++++++++++++++++++++++++++++++---------------------
>  2 files changed, 37 insertions(+), 25 deletions(-)
> 
> diff --git a/include/qemu/memfd.h b/include/qemu/memfd.h
> index 745a8c501e..41c24d807c 100644
> --- a/include/qemu/memfd.h
> +++ b/include/qemu/memfd.h
> @@ -16,6 +16,7 @@
>  #define F_SEAL_WRITE    0x0008  /* prevent writes */
>  #endif
>  
> +int qemu_memfd_create(const char *name, size_t size, unsigned int seals);
>  void *qemu_memfd_alloc(const char *name, size_t size, unsigned int seals,
>                         int *fd);
>  void qemu_memfd_free(void *ptr, size_t size, int fd);
> diff --git a/util/memfd.c b/util/memfd.c
> index 4571d1aba8..e9c1a0e700 100644
> --- a/util/memfd.c
> +++ b/util/memfd.c
> @@ -55,6 +55,38 @@ static int memfd_create(const char *name, unsigned int 
> flags)
>  #define MFD_ALLOW_SEALING 0x0002U
>  #endif
>  
> +int qemu_memfd_create(const char *name, size_t size, unsigned int seals)
> +{
> +    int mfd = -1;
> +
> +#ifdef CONFIG_LINUX
> +    unsigned int flags = MFD_CLOEXEC;
> +
> +    if (seals) {
> +        flags |= MFD_ALLOW_SEALING;

Reviewed-by: Philippe Mathieu-Daudé <address@hidden>

> +    }
> +
> +    mfd = memfd_create(name, flags);
> +    if (mfd < 0) {
> +        return -1;
> +    }
> +
> +    if (ftruncate(mfd, size) == -1) {
> +        perror("ftruncate");
> +        close(mfd);
> +        return -1;
> +    }
> +
> +    if (seals && fcntl(mfd, F_ADD_SEALS, seals) == -1) {
> +        perror("fcntl");
> +        close(mfd);
> +        return -1;
> +    }
> +#endif
> +
> +    return mfd;
> +}
> +
>  /*
>   * This is a best-effort helper for shared memory allocation, with
>   * optional sealing. The helper will do his best to allocate using
> @@ -65,35 +97,14 @@ void *qemu_memfd_alloc(const char *name, size_t size, 
> unsigned int seals,
>                         int *fd)
>  {
>      void *ptr;
> -    int mfd = -1;
> -
> -    *fd = -1;
> -
> -#ifdef CONFIG_LINUX
> -    if (seals) {
> -        mfd = memfd_create(name, MFD_ALLOW_SEALING | MFD_CLOEXEC);
> -    }
> +    int mfd = qemu_memfd_create(name, size, seals);
>  
> +    /* some systems have memfd without sealing */
>      if (mfd == -1) {
> -        /* some systems have memfd without sealing */
> -        mfd = memfd_create(name, MFD_CLOEXEC);
> -        seals = 0;
> +        mfd = qemu_memfd_create(name, size, 0);
>      }
> -#endif
> -
> -    if (mfd != -1) {
> -        if (ftruncate(mfd, size) == -1) {
> -            perror("ftruncate");
> -            close(mfd);
> -            return NULL;
> -        }
>  
> -        if (seals && fcntl(mfd, F_ADD_SEALS, seals) == -1) {
> -            perror("fcntl");
> -            close(mfd);
> -            return NULL;
> -        }
> -    } else {
> +    if (mfd == -1) {
>          const char *tmpdir = g_get_tmp_dir();
>          gchar *fname;
>  
>