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https://gitlab.freedesktop.org/wayland/weston
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![Sebastian Wick](/assets/img/avatar_default.png)
The ro_anonymous_file is an abstraction around anonymous read-only files.
os_ro_anonymous_file_create creates such a file with the contents passed
in data. Subsequent calls to os_ro_anonymous_file_get_fd return a fd
that's ready to be send over the socket.
When mapmode is RO_ANONYMOUS_FILE_MAPMODE_PRIVATE the fd is only
guaranteed to be mmap-able readonly with MAP_PRIVATE but does not
require duplicating the file for each resource when memfd_create is
available. RO_ANONYMOUS_FILE_MAPMODE_SHARED may be used when the client
must be able to map the file with MAP_SHARED but it also means that the
file has to be duplicated even when memfd_create is available.
See also:
weston commit 76829fc4ea
wayland commit 905c0a341ddf0a885811d19e2b79c65a3f1d210c
Signed-off-by: Sebastian Wick <sebastian@sebastianwick.net>
408 lines
9.6 KiB
C
408 lines
9.6 KiB
C
/*
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* Copyright © 2012 Collabora, Ltd.
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*
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* Permission is hereby granted, free of charge, to any person obtaining
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* a copy of this software and associated documentation files (the
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* "Software"), to deal in the Software without restriction, including
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* without limitation the rights to use, copy, modify, merge, publish,
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* distribute, sublicense, and/or sell copies of the Software, and to
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* permit persons to whom the Software is furnished to do so, subject to
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* the following conditions:
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*
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* The above copyright notice and this permission notice (including the
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* next paragraph) shall be included in all copies or substantial
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* portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
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* BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
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* ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
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* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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* SOFTWARE.
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*/
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#include "config.h"
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#include <sys/types.h>
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#include <sys/socket.h>
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#include <unistd.h>
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#include <fcntl.h>
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#include <errno.h>
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#include <sys/epoll.h>
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#include <string.h>
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#include <stdlib.h>
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#include <libweston/zalloc.h>
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#ifdef HAVE_MEMFD_CREATE
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#include <sys/mman.h>
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#endif
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#include "os-compatibility.h"
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#define READONLY_SEALS (F_SEAL_SHRINK | F_SEAL_GROW | F_SEAL_WRITE)
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int
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os_fd_set_cloexec(int fd)
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{
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long flags;
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if (fd == -1)
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return -1;
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flags = fcntl(fd, F_GETFD);
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if (flags == -1)
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return -1;
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if (fcntl(fd, F_SETFD, flags | FD_CLOEXEC) == -1)
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return -1;
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return 0;
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}
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static int
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set_cloexec_or_close(int fd)
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{
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if (os_fd_set_cloexec(fd) != 0) {
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close(fd);
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return -1;
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}
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return fd;
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}
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int
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os_socketpair_cloexec(int domain, int type, int protocol, int *sv)
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{
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int ret;
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#ifdef SOCK_CLOEXEC
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ret = socketpair(domain, type | SOCK_CLOEXEC, protocol, sv);
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if (ret == 0 || errno != EINVAL)
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return ret;
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#endif
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ret = socketpair(domain, type, protocol, sv);
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if (ret < 0)
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return ret;
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sv[0] = set_cloexec_or_close(sv[0]);
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sv[1] = set_cloexec_or_close(sv[1]);
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if (sv[0] != -1 && sv[1] != -1)
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return 0;
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close(sv[0]);
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close(sv[1]);
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return -1;
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}
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int
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os_epoll_create_cloexec(void)
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{
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int fd;
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#ifdef EPOLL_CLOEXEC
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fd = epoll_create1(EPOLL_CLOEXEC);
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if (fd >= 0)
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return fd;
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if (errno != EINVAL)
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return -1;
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#endif
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fd = epoll_create(1);
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return set_cloexec_or_close(fd);
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}
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static int
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create_tmpfile_cloexec(char *tmpname)
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{
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int fd;
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#ifdef HAVE_MKOSTEMP
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fd = mkostemp(tmpname, O_CLOEXEC);
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if (fd >= 0)
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unlink(tmpname);
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#else
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fd = mkstemp(tmpname);
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if (fd >= 0) {
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fd = set_cloexec_or_close(fd);
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unlink(tmpname);
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}
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#endif
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return fd;
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}
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/*
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* Create a new, unique, anonymous file of the given size, and
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* return the file descriptor for it. The file descriptor is set
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* CLOEXEC. The file is immediately suitable for mmap()'ing
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* the given size at offset zero.
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*
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* The file should not have a permanent backing store like a disk,
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* but may have if XDG_RUNTIME_DIR is not properly implemented in OS.
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*
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* The file name is deleted from the file system.
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*
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* The file is suitable for buffer sharing between processes by
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* transmitting the file descriptor over Unix sockets using the
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* SCM_RIGHTS methods.
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*
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* If the C library implements posix_fallocate(), it is used to
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* guarantee that disk space is available for the file at the
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* given size. If disk space is insufficient, errno is set to ENOSPC.
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* If posix_fallocate() is not supported, program may receive
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* SIGBUS on accessing mmap()'ed file contents instead.
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*
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* If the C library implements memfd_create(), it is used to create the
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* file purely in memory, without any backing file name on the file
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* system, and then sealing off the possibility of shrinking it. This
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* can then be checked before accessing mmap()'ed file contents, to
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* make sure SIGBUS can't happen. It also avoids requiring
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* XDG_RUNTIME_DIR.
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*/
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int
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os_create_anonymous_file(off_t size)
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{
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static const char template[] = "/weston-shared-XXXXXX";
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const char *path;
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char *name;
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int fd;
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int ret;
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#ifdef HAVE_MEMFD_CREATE
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fd = memfd_create("weston-shared", MFD_CLOEXEC | MFD_ALLOW_SEALING);
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if (fd >= 0) {
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/* We can add this seal before calling posix_fallocate(), as
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* the file is currently zero-sized anyway.
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*
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* There is also no need to check for the return value, we
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* couldn't do anything with it anyway.
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*/
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fcntl(fd, F_ADD_SEALS, F_SEAL_SHRINK);
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} else
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#endif
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{
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path = getenv("XDG_RUNTIME_DIR");
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if (!path) {
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errno = ENOENT;
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return -1;
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}
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name = malloc(strlen(path) + sizeof(template));
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if (!name)
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return -1;
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strcpy(name, path);
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strcat(name, template);
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fd = create_tmpfile_cloexec(name);
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free(name);
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if (fd < 0)
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return -1;
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}
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#ifdef HAVE_POSIX_FALLOCATE
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do {
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ret = posix_fallocate(fd, 0, size);
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} while (ret == EINTR);
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if (ret != 0) {
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close(fd);
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errno = ret;
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return -1;
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}
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#else
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do {
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ret = ftruncate(fd, size);
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} while (ret < 0 && errno == EINTR);
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if (ret < 0) {
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close(fd);
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return -1;
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}
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#endif
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return fd;
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}
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#ifndef HAVE_STRCHRNUL
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char *
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strchrnul(const char *s, int c)
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{
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while (*s && *s != c)
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s++;
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return (char *)s;
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}
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#endif
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struct ro_anonymous_file {
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int fd;
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size_t size;
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};
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/** Create a new anonymous read-only file of the given size and the given data
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*
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* \param size The size of \p data.
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* \param data The data of the file with the size \p size.
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* \return A new \c ro_anonymous_file, or NULL on failure.
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*
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* The intended use-case is for sending mid-sized data from the compositor
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* to clients.
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* If the function fails errno is set.
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*/
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struct ro_anonymous_file *
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os_ro_anonymous_file_create(size_t size,
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const char *data)
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{
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struct ro_anonymous_file *file;
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void *map;
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file = zalloc(sizeof *file);
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if (!file) {
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errno = ENOMEM;
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return NULL;
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}
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file->size = size;
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file->fd = os_create_anonymous_file(size);
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if (file->fd == -1)
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goto err_free;
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map = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, file->fd, 0);
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if (map == MAP_FAILED)
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goto err_close;
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memcpy(map, data, size);
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munmap(map, size);
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#ifdef HAVE_MEMFD_CREATE
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/* try to put seals on the file to make it read-only so that we can
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* return the fd later directly when support_shared is not set.
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* os_ro_anonymous_file_get_fd can handle the fd even if it is not
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* sealed read-only and will instead create a new anonymous file on
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* each invocation.
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*/
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fcntl(file->fd, F_ADD_SEALS, READONLY_SEALS);
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#endif
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return file;
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err_close:
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close(file->fd);
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err_free:
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free(file);
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return NULL;
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}
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/** Destroy an anonymous read-only file
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*
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* \param file The file to destroy.
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*/
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void
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os_ro_anonymous_file_destroy(struct ro_anonymous_file *file)
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{
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close(file->fd);
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free(file);
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}
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/** Get the size of an anonymous read-only file
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*
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* \param file The file to get the size of.
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* \return The size of the file.
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*/
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size_t
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os_ro_anonymous_file_size(struct ro_anonymous_file *file)
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{
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return file->size;
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}
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/** Returns a file descriptor for the given file, ready to be send to a client.
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*
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* \param file The file for which to get a file descriptor.
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* \param mapmode Describes the ways in which the returned file descriptor can
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* be used with mmap.
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* \return A file descriptor for the given file that can be send to a client
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* or -1 on failure.
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*
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* The returned file descriptor must not be shared between multiple clients.
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* When \p mapmode is RO_ANONYMOUS_FILE_MAPMODE_PRIVATE the file descriptor is
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* only guaranteed to be mmapable with \c MAP_PRIVATE, when \p mapmode is
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* RO_ANONYMOUS_FILE_MAPMODE_SHARED the file descriptor can be mmaped with
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* either MAP_PRIVATE or MAP_SHARED.
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* When you're done with the fd you must call \c os_ro_anonymous_file_put_fd
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* instead of calling \c close.
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* If the function fails errno is set.
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*/
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int
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os_ro_anonymous_file_get_fd(struct ro_anonymous_file *file,
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enum ro_anonymous_file_mapmode mapmode)
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{
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void *src, *dst;
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int seals, fd;
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seals = fcntl(file->fd, F_GET_SEALS);
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/* file was sealed for read-only and we don't have to support MAP_SHARED
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* so we can simply pass the memfd fd
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*/
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if (seals != -1 && mapmode == RO_ANONYMOUS_FILE_MAPMODE_PRIVATE &&
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(seals & READONLY_SEALS) == READONLY_SEALS)
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return file->fd;
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/* for all other cases we create a new anonymous file that can be mapped
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* with MAP_SHARED and copy the contents to it and return that instead
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*/
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fd = os_create_anonymous_file(file->size);
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if (fd == -1)
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return fd;
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src = mmap(NULL, file->size, PROT_READ, MAP_PRIVATE, file->fd, 0);
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if (src == MAP_FAILED) {
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close(fd);
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return -1;
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}
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dst = mmap(NULL, file->size, PROT_WRITE, MAP_SHARED, fd, 0);
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if (dst == MAP_FAILED) {
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close(fd);
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munmap(src, file->size);
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return -1;
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}
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memcpy(dst, src, file->size);
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munmap(src, file->size);
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munmap(dst, file->size);
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return fd;
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}
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/** Release a file descriptor returned by \c os_ro_anonymous_file_get_fd
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*
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* \param fd A file descriptor returned by \c os_ro_anonymous_file_get_fd.
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* \return 0 on success, or -1 on failure.
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*
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* This function must be called for every file descriptor created with
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* \c os_ro_anonymous_file_get_fd to not leake any resources.
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* If the function fails errno is set.
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*/
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int
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os_ro_anonymous_file_put_fd(int fd)
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{
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int seals = fcntl(fd, F_GET_SEALS);
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if (seals == -1 && errno != EINVAL)
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return -1;
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/* If the fd cannot be sealed seals is -1 at this point
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* or the file can be sealed but has not been sealed for writing.
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* In both cases we created a new anonymous file that we have to
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* close.
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*/
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if (seals == -1 || !(seals & F_SEAL_WRITE))
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close(fd);
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return 0;
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}
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