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util: use SCM_RIGHTS in virFileOperation when needed
Currently, the hook function in virFileOperation is extremely limited: it must be async-signal-safe, and cannot modify any memory in the parent process. It is much handier to return a valid fd and operate on it in the parent than to deal with hook restrictions. * src/util/util.h (VIR_FILE_OP_RETURN_FD): New flag. * src/util/util.c (virFileOperationNoFork, virFileOperation): Honor new flag.
This commit is contained in:
Eric Blake
parent
9497506fa0
commit
055d4ff87c
138
src/util/util.c
138
src/util/util.c
@ -1428,14 +1428,15 @@ static int virFileOperationNoFork(const char *path, int openflags, mode_t mode,
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if ((hook) && ((ret = hook(fd, hookdata)) != 0)) {
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goto error;
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}
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if (flags & VIR_FILE_OP_RETURN_FD)
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return fd;
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if (VIR_CLOSE(fd) < 0) {
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ret = -errno;
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virReportSystemError(errno, _("failed to close new file '%s'"),
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path);
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fd = -1;
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goto error;
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}
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fd = -1;
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error:
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VIR_FORCE_CLOSE(fd);
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return ret;
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@ -1480,7 +1481,32 @@ error:
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return ret;
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}
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/* return -errno on failure, or 0 on success */
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/**
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* virFileOperation:
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* @path: file to open or create
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* @openflags: flags to pass to open
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* @mode: mode to use on creation or when forcing permissions
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* @uid: uid that should own file on creation
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* @gid: gid that should own file
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* @hook: callback to run once file is open; see below for restrictions
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* @hookdata: opaque data for @hook
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* @flags: bit-wise or of VIR_FILE_OP_* flags
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*
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* Open @path, and execute an optional callback @hook on the open file
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* description. @hook must return 0 on success, or -errno on failure.
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* If @flags includes VIR_FILE_OP_AS_UID, then open the file while the
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* effective user id is @uid (by using a child process); this allows
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* one to bypass root-squashing NFS issues. If @flags includes
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* VIR_FILE_OP_FORCE_PERMS, then ensure that @path has those
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* permissions before the callback, even if the file already existed
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* with different permissions. If @flags includes
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* VIR_FILE_OP_RETURN_FD, then use SCM_RIGHTS to guarantee that any
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* @hook is run in the parent, and the return value (if non-negative)
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* is the file descriptor, left open. Otherwise, @hook might be run
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* in a child process, so it must be async-signal-safe (ie. no
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* malloc() or anything else that depends on modifying locks held in
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* the parent), no file descriptor remains open, and 0 is returned on
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* success. Return -errno on failure. */
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int virFileOperation(const char *path, int openflags, mode_t mode,
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uid_t uid, gid_t gid,
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virFileOperationHook hook, void *hookdata,
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@ -1488,7 +1514,14 @@ int virFileOperation(const char *path, int openflags, mode_t mode,
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struct stat st;
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pid_t pid;
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int waitret, status, ret = 0;
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int fd;
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int fd = -1;
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int pair[2] = { -1, -1 };
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struct msghdr msg;
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struct cmsghdr *cmsg;
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char buf[CMSG_SPACE(sizeof(fd))];
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char dummy = 0;
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struct iovec iov;
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int forkRet;
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if ((!(flags & VIR_FILE_OP_AS_UID))
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|| (getuid() != 0)
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@ -1502,7 +1535,29 @@ int virFileOperation(const char *path, int openflags, mode_t mode,
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* following dance avoids problems caused by root-squashing
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* NFS servers. */
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int forkRet = virFork(&pid);
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if (flags & VIR_FILE_OP_RETURN_FD) {
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if (socketpair(AF_UNIX, SOCK_STREAM, 0, pair) < 0) {
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ret = -errno;
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virReportSystemError(errno,
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_("failed to create socket needed for '%s'"),
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path);
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return ret;
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}
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memset(&msg, 0, sizeof(msg));
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iov.iov_base = &dummy;
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iov.iov_len = 1;
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msg.msg_iov = &iov;
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msg.msg_iovlen = 1;
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msg.msg_control = buf;
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msg.msg_controllen = sizeof(buf);
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cmsg = CMSG_FIRSTHDR(&msg);
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cmsg->cmsg_level = SOL_SOCKET;
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cmsg->cmsg_type = SCM_RIGHTS;
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cmsg->cmsg_len = CMSG_LEN(sizeof(fd));
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}
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forkRet = virFork(&pid);
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if (pid < 0) {
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ret = -errno;
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@ -1510,6 +1565,31 @@ int virFileOperation(const char *path, int openflags, mode_t mode,
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}
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if (pid) { /* parent */
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if (flags & VIR_FILE_OP_RETURN_FD) {
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VIR_FORCE_CLOSE(pair[1]);
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do {
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ret = recvmsg(pair[0], &msg, 0);
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} while (ret < 0 && errno == EINTR);
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if (ret < 0) {
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ret = -errno;
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VIR_FORCE_CLOSE(pair[0]);
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while ((waitret = waitpid(pid, NULL, 0) == -1)
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&& (errno == EINTR));
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goto parenterror;
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}
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VIR_FORCE_CLOSE(pair[0]);
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/* See if fd was transferred. */
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cmsg = CMSG_FIRSTHDR(&msg);
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if (cmsg && cmsg->cmsg_len == CMSG_LEN(sizeof(fd)) &&
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cmsg->cmsg_level == SOL_SOCKET &&
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cmsg->cmsg_type == SCM_RIGHTS) {
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memcpy(&fd, CMSG_DATA(cmsg), sizeof(fd));
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}
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}
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/* wait for child to complete, and retrieve its exit code */
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while ((waitret = waitpid(pid, &status, 0) == -1)
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&& (errno == EINTR));
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@ -1520,12 +1600,20 @@ int virFileOperation(const char *path, int openflags, mode_t mode,
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path);
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goto parenterror;
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}
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if (!WIFEXITED(status) || (ret = -WEXITSTATUS(status)) == -EACCES) {
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if (!WIFEXITED(status) || (ret = -WEXITSTATUS(status)) == -EACCES ||
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((flags & VIR_FILE_OP_RETURN_FD) && fd == -1)) {
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/* fall back to the simpler method, which works better in
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* some cases */
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return virFileOperationNoFork(path, openflags, mode, uid, gid,
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hook, hookdata, flags);
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}
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if (!ret && (flags & VIR_FILE_OP_RETURN_FD)) {
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if ((hook) && ((ret = hook(fd, hookdata)) != 0)) {
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VIR_FORCE_CLOSE(fd);
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goto parenterror;
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}
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ret = fd;
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}
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parenterror:
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return ret;
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}
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@ -1535,6 +1623,7 @@ parenterror:
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if (forkRet < 0) {
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/* error encountered and logged in virFork() after the fork. */
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ret = -errno;
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goto childerror;
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}
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@ -1584,15 +1673,32 @@ parenterror:
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path, mode);
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goto childerror;
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}
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if ((hook) && ((ret = hook(fd, hookdata)) != 0)) {
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goto childerror;
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}
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if (VIR_CLOSE(fd) < 0) {
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ret = -errno;
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virReportSystemError(errno, _("child failed to close new file '%s'"),
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path);
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goto childerror;
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if (flags & VIR_FILE_OP_RETURN_FD) {
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VIR_FORCE_CLOSE(pair[0]);
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memcpy(CMSG_DATA(cmsg), &fd, sizeof(fd));
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do {
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ret = sendmsg(pair[1], &msg, 0);
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} while (ret < 0 && errno == EINTR);
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if (ret < 0) {
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ret = -errno;
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goto childerror;
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}
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ret = 0;
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} else {
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if ((hook) && ((ret = hook(fd, hookdata)) != 0))
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goto childerror;
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if (VIR_CLOSE(fd) < 0) {
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ret = -errno;
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virReportSystemError(errno,
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_("child failed to close new file '%s'"),
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path);
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goto childerror;
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}
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}
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ret = 0;
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childerror:
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/* ret tracks -errno on failure, but exit value must be positive.
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* If the child exits with EACCES, then the parent tries again. */
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@ -1719,7 +1825,7 @@ int virFileOperation(const char *path ATTRIBUTE_UNUSED,
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virUtilError(VIR_ERR_INTERNAL_ERROR,
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"%s", _("virFileOperation is not implemented for WIN32"));
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return -1;
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return -ENOSYS;
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}
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int virDirCreate(const char *path ATTRIBUTE_UNUSED,
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@ -1731,7 +1837,7 @@ int virDirCreate(const char *path ATTRIBUTE_UNUSED,
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virUtilError(VIR_ERR_INTERNAL_ERROR,
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"%s", _("virDirCreate is not implemented for WIN32"));
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return -1;
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return -ENOSYS;
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}
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#endif /* WIN32 */
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@ -130,12 +130,14 @@ enum {
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VIR_FILE_OP_NONE = 0,
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VIR_FILE_OP_AS_UID = (1 << 0),
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VIR_FILE_OP_FORCE_PERMS = (1 << 1),
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VIR_FILE_OP_RETURN_FD = (1 << 2),
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};
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typedef int (*virFileOperationHook)(int fd, void *data);
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int virFileOperation(const char *path, int openflags, mode_t mode,
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uid_t uid, gid_t gid,
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virFileOperationHook hook, void *hookdata,
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unsigned int flags) ATTRIBUTE_RETURN_CHECK;
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unsigned int flags)
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ATTRIBUTE_NONNULL(1) ATTRIBUTE_RETURN_CHECK;
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enum {
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VIR_DIR_CREATE_NONE = 0,
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