011b695403
If posix_fallocate is available, use it instead of ftruncate. Unlike ftruncate, when posix_fallocate succeeds, it guarantees that you cannot run out of disk space, when later writing to the mmap()'ed file. With posix_fallocate, if os_create_anonymous_file() succeeds, the program cannot get a SIGBUS later from accessing this file via mmap. If there is insufficient disk space, the function fails and errno is set to ENOSPC. This is useful on systems, that limit the available buffer space by having XDG_RUNTIME_DIR on a small tmpfs. Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
146 lines
3.4 KiB
C
146 lines
3.4 KiB
C
/*
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* Copyright © 2012 Collabora, Ltd.
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*
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* Permission to use, copy, modify, distribute, and sell this software and its
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* documentation for any purpose is hereby granted without fee, provided that
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* the above copyright notice appear in all copies and that both that copyright
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* notice and this permission notice appear in supporting documentation, and
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* that the name of the copyright holders not be used in advertising or
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* publicity pertaining to distribution of the software without specific,
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* written prior permission. The copyright holders make no representations
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* about the suitability of this software for any purpose. It is provided "as
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* is" without express or implied warranty.
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*
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* THE COPYRIGHT HOLDERS DISCLAIM ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
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* INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO
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* EVENT SHALL THE COPYRIGHT HOLDERS BE LIABLE FOR ANY SPECIAL, INDIRECT OR
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* CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE,
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* DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
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* TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE
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* OF THIS SOFTWARE.
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*/
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#define _GNU_SOURCE
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#include <sys/types.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 <string.h>
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#include <stdlib.h>
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#include "config.h"
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#include "os-compatibility.h"
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#ifndef HAVE_MKOSTEMP
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static int
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set_cloexec_or_close(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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goto err;
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if (fcntl(fd, F_SETFD, flags | FD_CLOEXEC) == -1)
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goto err;
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return fd;
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err:
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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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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 insufficent, 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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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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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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#ifdef HAVE_POSIX_FALLOCATE
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ret = posix_fallocate(fd, 0, size);
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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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ret = ftruncate(fd, size);
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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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