Re: [Qemu-devel] [PATCH RFC 2/6] posix: add linux-only memfd fallback

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Jul 23, 2015 at 03:36:39AM +0200, Marc-André Lureau wrote:
> Implement memfd_create() fallback if not available in system libc.
> memfd_create() is still not included in glibc today, atlhough it's been
> available since Linux 3.17 in Oct 2014.
> 
> memfd has numerous advantages over traditional shm/mmap for ipc memory
> sharing with fd handler, which we are going to make use of for
> vhost-user logging memory in following patches.
> 
> Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> ---
>  include/qemu/osdep.h | 59 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 59 insertions(+)
> 
> diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
> index 3247364..adc138b 100644
> --- a/include/qemu/osdep.h
> +++ b/include/qemu/osdep.h
> @@ -6,6 +6,7 @@
>  #include <stddef.h>
>  #include <stdbool.h>
>  #include <stdint.h>
> +#include <unistd.h>
>  #include <sys/types.h>
>  #ifdef __OpenBSD__
>  #include <sys/signal.h>
> @@ -20,6 +21,64 @@
>  
>  #include <sys/time.h>
>  
> +#ifdef CONFIG_LINUX
> +
> +#ifndef F_LINUX_SPECIFIC_BASE
> +#define F_LINUX_SPECIFIC_BASE 1024
> +#endif
> +
> +#ifndef F_ADD_SEALS
> +#define F_ADD_SEALS (F_LINUX_SPECIFIC_BASE + 9)
> +#define F_GET_SEALS (F_LINUX_SPECIFIC_BASE + 10)
> +
> +#define F_SEAL_SEAL     0x0001  /* prevent further seals from being set */
> +#define F_SEAL_SHRINK   0x0002  /* prevent file from shrinking */
> +#define F_SEAL_GROW     0x0004  /* prevent file from growing */
> +#define F_SEAL_WRITE    0x0008  /* prevent writes */
> +#endif

These are from include/uapi/linux/fcntl.h,
they should be imported into linux-headers I think.

> +
> +#ifndef MFD_ALLOW_SEALING
> +#define MFD_ALLOW_SEALING 0x0002U
> +#endif
> +
> +#ifndef MFD_CLOEXEC
> +#define MFD_CLOEXEC 0x0001U
> +#endif
> +
> +#ifndef __NR_memfd_create
> +#  if defined __x86_64__
> +#    define __NR_memfd_create 319
> +#  elif defined __arm__
> +#    define __NR_memfd_create 385
> +#  elif defined __aarch64__
> +#    define __NR_memfd_create 279
> +#  elif defined _MIPS_SIM
> +#    if _MIPS_SIM == _MIPS_SIM_ABI32
> +#      define __NR_memfd_create 4354
> +#    endif
> +#    if _MIPS_SIM == _MIPS_SIM_NABI32
> +#      define __NR_memfd_create 6318
> +#    endif
> +#    if _MIPS_SIM == _MIPS_SIM_ABI64
> +#      define __NR_memfd_create 5314
> +#    endif

What's defining all these macros?

> +#  elif defined __i386__
> +#    define __NR_memfd_create 356
> +#  else
> +#    warning "__NR_memfd_create unknown for your architecture"
> +#    define __NR_memfd_create 0xffffffff
> +#  endif
> +#endif
> +
> +#ifndef CONFIG_MEMFD
> +static inline int memfd_create(const char *name, unsigned int flags)
> +{
> +        return syscall(__NR_memfd_create, name, flags);
> +}
> +#endif

How about making these non-inline?

I think we need stubs for non-posix systems, right?

> +
> +#endif /* LINUX */
> +
>  #if defined(CONFIG_SOLARIS) && CONFIG_SOLARIS_VERSION < 10
>  /* [u]int_fast*_t not in <sys/int_types.h> */
>  typedef unsigned char           uint_fast8_t;
> -- 
> 2.4.3