qemu

memfd.c (5083B)

---

 /*
  * memfd.c
  *
  * Copyright (c) 2015 Red Hat, Inc.
  *
  * QEMU library functions on POSIX which are shared between QEMU and
  * the QEMU tools.
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
  * in the Software without restriction, including without limitation the rights
  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  * copies of the Software, and to permit persons to whom the Software is
  * furnished to do so, subject to the following conditions:
  *
  * The above copyright notice and this permission notice shall be included in
  * all copies or substantial portions of the Software.
  *
  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  * THE SOFTWARE.
  */
 
 #include "qemu/osdep.h"
 
 #include "qapi/error.h"
 #include "qemu/memfd.h"
 #include "qemu/host-utils.h"
 
 #if defined CONFIG_LINUX && !defined CONFIG_MEMFD
 #include <sys/syscall.h>
 #include <asm/unistd.h>
 
 int memfd_create(const char *name, unsigned int flags)
 {
 #ifdef __NR_memfd_create
     return syscall(__NR_memfd_create, name, flags);
 #else
     errno = ENOSYS;
     return -1;
 #endif
 }
 #endif
 
 int qemu_memfd_create(const char *name, size_t size, bool hugetlb,
                       uint64_t hugetlbsize, unsigned int seals, Error **errp)
 {
     int htsize = hugetlbsize ? ctz64(hugetlbsize) : 0;
 
     if (htsize && 1ULL << htsize != hugetlbsize) {
         error_setg(errp, "Hugepage size must be a power of 2");
         return -1;
     }
 
     htsize = htsize << MFD_HUGE_SHIFT;
 
 #ifdef CONFIG_LINUX
     int mfd = -1;
     unsigned int flags = MFD_CLOEXEC;
 
     if (seals) {
         flags |= MFD_ALLOW_SEALING;
     }
     if (hugetlb) {
         flags |= MFD_HUGETLB;
         flags |= htsize;
     }
     mfd = memfd_create(name, flags);
     if (mfd < 0) {
         error_setg_errno(errp, errno,
                          "failed to create memfd with flags 0x%x", flags);
         goto err;
     }
 
     if (ftruncate(mfd, size) == -1) {
         error_setg_errno(errp, errno, "failed to resize memfd to %zu", size);
         goto err;
     }
 
     if (seals && fcntl(mfd, F_ADD_SEALS, seals) == -1) {
         error_setg_errno(errp, errno, "failed to add seals 0x%x", seals);
         goto err;
     }
 
     return mfd;
 
 err:
     if (mfd >= 0) {
         close(mfd);
     }
 #else
     error_setg_errno(errp, ENOSYS, "failed to create memfd");
 #endif
     return -1;
 }
 
 /*
  * 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, Error **errp)
 {
     void *ptr;
     int mfd = qemu_memfd_create(name, size, false, 0, seals, NULL);
 
     /* some systems have memfd without sealing */
     if (mfd == -1) {
         mfd = qemu_memfd_create(name, size, false, 0, 0, NULL);
     }
 
     if (mfd == -1) {
         const char *tmpdir = g_get_tmp_dir();
         gchar *fname;
 
         fname = g_strdup_printf("%s/memfd-XXXXXX", tmpdir);
         mfd = mkstemp(fname);
         unlink(fname);
         g_free(fname);
 
         if (mfd == -1 ||
             ftruncate(mfd, size) == -1) {
             goto err;
         }
     }
 
     ptr = mmap(0, size, PROT_READ | PROT_WRITE, MAP_SHARED, mfd, 0);
     if (ptr == MAP_FAILED) {
         goto err;
     }
 
     *fd = mfd;
     return ptr;
 
 err:
     error_setg_errno(errp, errno, "failed to allocate shared memory");
     if (mfd >= 0) {
         close(mfd);
     }
     return NULL;
 }
 
 void qemu_memfd_free(void *ptr, size_t size, int fd)
 {
     if (ptr) {
         munmap(ptr, size);
     }
 
     if (fd != -1) {
         close(fd);
     }
 }
 
 enum {
     MEMFD_KO,
     MEMFD_OK,
     MEMFD_TODO
 };
 
 /**
  * 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;
 
     if (memfd_check == MEMFD_TODO) {
         int fd;
         void *ptr;
 
         fd = -1;
         ptr = qemu_memfd_alloc("test", 4096, 0, &fd, NULL);
         memfd_check = ptr ? MEMFD_OK : MEMFD_KO;
         qemu_memfd_free(ptr, 4096, fd);
     }
 
     return memfd_check == MEMFD_OK;
 }
 
 /**
  * qemu_memfd_check():
  *
  * Check if host supports memfd.
  */
 bool qemu_memfd_check(unsigned int flags)
 {
 #ifdef CONFIG_LINUX
     int mfd = memfd_create("test", flags | MFD_CLOEXEC);
 
     if (mfd >= 0) {
         close(mfd);
         return true;
     }
 #endif
 
     return false;
 }