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#include <errno.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <time.h>
#include <unistd.h>
#include "shm.h"
/* These two functions aren't used on linux. */
#ifndef __linux__
static void randname(char *buf)
{
struct timespec ts;
clock_gettime(CLOCK_REALTIME, &ts);
long r = ts.tv_nsec;
for (int i = 0; i < 6; ++i) {
buf[i] = 'A'+(r&15)+(r&16)*2;
r >>= 5;
}
}
static int create_shm_file(void)
{
int retries = 100;
do {
char name[] = "/wl_shm-XXXXXX";
randname(name + sizeof(name) - 7);
--retries;
int fd = shm_open(name, O_RDWR | O_CREAT | O_EXCL, 0600);
if (fd >= 0) {
shm_unlink(name);
return fd;
}
} while (retries > 0 && errno == EEXIST);
return -1;
}
#endif
int shm_allocate_file(size_t size)
{
#ifdef __linux__
/*
* On linux, we can just use memfd_create(). This is both simpler and
* potentially allows usage of Transparent HugePages, which speed up
* the first paint of a large screen buffer.
*
* This isn't available on *BSD, which we could conceivably be running
* on.
*/
int fd = memfd_create("wl_shm", 0);
#else
int fd = create_shm_file();
#endif
if (fd < 0)
return -1;
int ret;
do {
ret = ftruncate(fd, size);
} while (ret < 0 && errno == EINTR);
if (ret < 0) {
close(fd);
return -1;
}
return fd;
}
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