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#include <sys/mman.h>
#include <unistd.h>
#include <fcntl.h>
#include <assert.h>
#include <cstdlib>
#include <cstring>
#include <cerrno>
#include "utils.h"
static int
os_fd_set_cloexec(int fd)
{
long flags;
if (fd == -1)
return -1;
flags = fcntl(fd, F_GETFD);
if (flags == -1)
return -1;
if (fcntl(fd, F_SETFD, flags | FD_CLOEXEC) == -1)
return -1;
return 0;
}
static int
set_cloexec_or_close(int fd)
{
if (os_fd_set_cloexec(fd) != 0) {
close(fd);
return -1;
}
return fd;
}
static int
create_tmpfile_cloexec(char *tmpname)
{
int fd;
#ifdef HAVE_MKOSTEMP
fd = mkostemp(tmpname, O_CLOEXEC);
if (fd >= 0)
unlink(tmpname);
#else
fd = mkstemp(tmpname);
if (fd >= 0) {
fd = set_cloexec_or_close(fd);
unlink(tmpname);
}
#endif
return fd;
}
/*
* Create a new, unique, anonymous file of the given size, and
* return the file descriptor for it. The file descriptor is set
* CLOEXEC. The file is immediately suitable for mmap()'ing
* the given size at offset zero.
*
* The file should not have a permanent backing store like a disk,
* but may have if XDG_RUNTIME_DIR is not properly implemented in OS.
*
* The file name is deleted from the file system.
*
* The file is suitable for buffer sharing between processes by
* transmitting the file descriptor over Unix sockets using the
* SCM_RIGHTS methods.
*
* If the C library implements posix_fallocate(), it is used to
* guarantee that disk space is available for the file at the
* given size. If disk space is insufficient, errno is set to ENOSPC.
* If posix_fallocate() is not supported, program may receive
* SIGBUS on accessing mmap()'ed file contents instead.
*
* If the C library implements memfd_create(), it is used to create the
* file purely in memory, without any backing file name on the file
* system, and then sealing off the possibility of shrinking it. This
* can then be checked before accessing mmap()'ed file contents, to
* make sure SIGBUS can't happen. It also avoids requiring
* XDG_RUNTIME_DIR.
*/
int
os_create_anonymous_file(off_t size)
{
static const char weston_template[] = "/weston-shared-XXXXXX";
const char *path;
char *name;
int fd;
int ret;
#ifdef HAVE_MEMFD_CREATE
fd = memfd_create("weston-shared", MFD_CLOEXEC | MFD_ALLOW_SEALING);
if (fd >= 0) {
/* We can add this seal before calling posix_fallocate(), as
* the file is currently zero-sized anyway.
*
* There is also no need to check for the return value, we
* couldn't do anything with it anyway.
*/
fcntl(fd, F_ADD_SEALS, F_SEAL_SHRINK);
} else
#endif
{
path = getenv("XDG_RUNTIME_DIR");
if (!path) {
errno = ENOENT;
return -1;
}
name = static_cast<char *>(malloc(strlen(path) + sizeof(weston_template)));
if (!name)
return -1;
strcpy(name, path);
strcat(name, weston_template);
fd = create_tmpfile_cloexec(name);
free(name);
if (fd < 0)
return -1;
}
#ifdef HAVE_POSIX_FALLOCATE
do {
ret = posix_fallocate(fd, 0, size);
} while (ret == EINTR);
if (ret != 0) {
close(fd);
errno = ret;
return -1;
}
#else
do {
ret = ftruncate(fd, size);
} while (ret < 0 && errno == EINTR);
if (ret < 0) {
close(fd);
return -1;
}
#endif
return fd;
}
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