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util: add memfd helpers

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Add qemu_memfd_alloc/free() helpers.

The function helps to allocate and seal shared memory.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Tested-by: Thibaut Collet <thibaut.collet@6wind.com>
This commit is contained in:
Marc-André Lureau 2015-10-09 17:17:20 +02:00 committed by Michael S. Tsirkin
parent f04cf9239a
commit d3592199ba
2 changed files with 75 additions and 1 deletions
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4
include/qemu/memfd.h
View File

@ -17,4 +17,8 @@
#define F_SEAL_WRITE 0x0008 /* prevent writes */
#endif
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);
#endif /* QEMU_MEMFD_H */

72
util/memfd.c
View File

@ -27,6 +27,11 @@
#include "qemu/osdep.h"
#include <glib.h>
#include <glib/gprintf.h>
#include <sys/mman.h>
#include "qemu/memfd.h"
#ifdef CONFIG_MEMFD
@ -35,7 +40,7 @@
#include <sys/syscall.h>
#include <asm/unistd.h>
inline static int memfd_create(const char *name, unsigned int flags)
static int memfd_create(const char *name, unsigned int flags)
{
#ifdef __NR_memfd_create
return syscall(__NR_memfd_create, name, flags);
@ -52,3 +57,68 @@ inline static int memfd_create(const char *name, unsigned int flags)
#ifndef MFD_ALLOW_SEALING
#define MFD_ALLOW_SEALING 0x0002U
#endif
/*
* This is a best-effort helper for shared memory allocation, with
* optional sealing. The helper will do his best to allocate using
* memfd with sealing, but may fallback on other methods without
* sealing.
*/
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);
}
if (mfd == -1) {
/* some systems have memfd without sealing */
mfd = memfd_create(name, MFD_CLOEXEC);
seals = 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 {
perror("memfd");
return NULL;
}
ptr = mmap(0, size, PROT_READ | PROT_WRITE, MAP_SHARED, mfd, 0);
if (ptr == MAP_FAILED) {
perror("mmap");
close(mfd);
return NULL;
}
*fd = mfd;
return ptr;
}
void qemu_memfd_free(void *ptr, size_t size, int fd)
{
if (ptr) {
munmap(ptr, size);
}
if (fd != -1) {
close(fd);
}
}