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Use posix_spawn instead of fork+exec

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Client code might allocate a lot of memory before starting the mount.
Fork is slow for processes that are using a lot of memory.  But
posix_spawn fixes that.

Another issue with fork is if the process is also doing RDMA - this
might lead to data corruption, as least if memory used for RDMA
is not marked with MADV_DONTFORK.  At least with linux kernels
before 5.12.
Also see https://blog.nelhage.com/post/a-cursed-bug/ for more details

Change by Bernd:
This also prepares the new fusermount option "--comm-fd", but keeps
the previous way to pass the parameter as env variable. In a future
release (exact data to be determined) we are going to remove usage
of the env variable and will switch to the new parameter.
This commit is contained in:
Matthias Goergens
2024-03-05 15:10:21 +01:00
committed by Bernd Schubert
parent 9e35addc35
commit bb9cecbf67
2 changed files with 102 additions and 101 deletions
Download Patch File Download Diff File Expand all files Collapse all files
lib/mount.c
+88 -92
View File
@@ -8,6 +8,9 @@
See the file COPYING.LIB.
*/
/* For environ */
#define _GNU_SOURCE
#include "fuse_config.h"
#include "fuse_i.h"
#include "fuse_misc.h"
@@ -22,6 +25,7 @@
#include <fcntl.h>
#include <errno.h>
#include <poll.h>
#include <spawn.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <sys/wait.h>
@@ -44,10 +48,6 @@
#define FUSERMOUNT_PROG "fusermount3"
#define FUSE_COMMFD_ENV "_FUSE_COMMFD"
#ifndef HAVE_FORK
#define fork() vfork()
#endif
#ifndef MS_DIRSYNC
#define MS_DIRSYNC 128
#endif
@@ -117,20 +117,17 @@ static const struct fuse_opt fuse_mount_opts[] = {
FUSE_OPT_END
};
static void exec_fusermount(const char *argv[])
{
execv(FUSERMOUNT_DIR "/" FUSERMOUNT_PROG, (char **) argv);
execvp(FUSERMOUNT_PROG, (char **) argv);
}
void fuse_mount_version(void)
{
int pid = fork();
if (!pid) {
const char *argv[] = { FUSERMOUNT_PROG, "--version", NULL };
exec_fusermount(argv);
_exit(1);
} else if (pid != -1)
char const *const argv[] = {FUSERMOUNT_PROG, "--version", NULL};
pid_t pid;
int status = posix_spawn(&pid, FUSERMOUNT_DIR "/" FUSERMOUNT_PROG, NULL,
NULL, (char * const *) argv, environ)
&& posix_spawnp(&pid, FUSERMOUNT_PROG, NULL,
NULL, (char * const *) argv, environ);
if(status != 0)
perror("posix_spawn");
else
waitpid(pid, NULL, 0);
}
@@ -269,7 +266,7 @@ static int receive_fd(int fd)
void fuse_kern_unmount(const char *mountpoint, int fd)
{
int res;
int pid;
pid_t pid;
if (fd != -1) {
struct pollfd pfd;
@@ -301,23 +298,24 @@ void fuse_kern_unmount(const char *mountpoint, int fd)
if (res == 0)
return;
pid = fork();
if(pid == -1)
return;
if(pid == 0) {
const char *argv[] = { FUSERMOUNT_PROG, "-u", "-q", "-z",
char const * const argv[] =
{ FUSERMOUNT_PROG, "--unmount", "--quiet", "--lazy",
"--", mountpoint, NULL };
exec_fusermount(argv);
_exit(1);
int status = posix_spawn(
&pid, FUSERMOUNT_DIR "/" FUSERMOUNT_PROG, NULL, NULL, (char * const *) argv, environ)
&& posix_spawnp(
&pid, FUSERMOUNT_PROG, NULL, NULL, (char * const *) argv, environ);
if(status != 0) {
perror("posix_spawn");
return;
}
waitpid(pid, NULL, 0);
}
static int setup_auto_unmount(const char *mountpoint, int quiet)
{
int fds[2], pid;
int fds[2];
pid_t pid;
int res;
if (!mountpoint) {
@@ -331,55 +329,55 @@ static int setup_auto_unmount(const char *mountpoint, int quiet)
return -1;
}
pid = fork();
if(pid == -1) {
perror("fuse: fork() failed");
close(fds[0]);
close(fds[1]);
return -1;
}
char arg_fd_entry[30];
snprintf(arg_fd_entry, sizeof(arg_fd_entry), "%i", fds[0]);
setenv(FUSE_COMMFD_ENV, arg_fd_entry, 1);
if(pid == 0) {
char env[10];
const char *argv[32];
int a = 0;
char const *const argv[] = {
FUSERMOUNT_PROG,
"--auto-unmount",
"--",
mountpoint,
NULL,
};
// TODO: add error handling for all manipulations of action.
posix_spawn_file_actions_t action;
posix_spawn_file_actions_init(&action);
if (quiet) {
int fd = open("/dev/null", O_RDONLY);
if (fd != -1) {
dup2(fd, 1);
dup2(fd, 2);
}
posix_spawn_file_actions_addclose(&action, 1);
posix_spawn_file_actions_addclose(&action, 2);
}
posix_spawn_file_actions_addclose(&action, fds[1]);
argv[a++] = FUSERMOUNT_PROG;
argv[a++] = "--auto-unmount";
argv[a++] = "--";
argv[a++] = mountpoint;
argv[a++] = NULL;
int status = posix_spawn(&pid, FUSERMOUNT_DIR "/" FUSERMOUNT_PROG, &action,
NULL, (char *const *) argv, environ)
&& posix_spawnp(&pid, FUSERMOUNT_PROG, &action,
NULL, (char *const *) argv, environ);
posix_spawn_file_actions_destroy(&action);
if(status != 0) {
close(fds[0]);
close(fds[1]);
fcntl(fds[0], F_SETFD, 0);
snprintf(env, sizeof(env), "%i", fds[0]);
setenv(FUSE_COMMFD_ENV, env, 1);
exec_fusermount(argv);
perror("fuse: failed to exec fusermount3");
_exit(1);
perror("fuse: posix_spawnp() of fusermount3 failed");
return -1;
}
// passed to child now, so can close here.
close(fds[0]);
// Now fusermount3 will only exit when fds[1] closes automatically when our
// process exits.
return 0;
// Note: fds[1] is leakend and doesn't get FD_CLOEXEC
}
static int fuse_mount_fusermount(const char *mountpoint, struct mount_opts *mo,
const char *opts, int quiet)
{
int fds[2], pid;
int fds[2];
pid_t pid;
int res;
int rv;
if (!mountpoint) {
fuse_log(FUSE_LOG_ERR, "fuse: missing mountpoint parameter\n");
@@ -392,47 +390,45 @@ static int fuse_mount_fusermount(const char *mountpoint, struct mount_opts *mo,
return -1;
}
pid = fork();
if(pid == -1) {
perror("fuse: fork() failed");
char arg_fd_entry[30];
snprintf(arg_fd_entry, sizeof(arg_fd_entry), "%i", fds[0]);
setenv(FUSE_COMMFD_ENV, arg_fd_entry, 1);
char const *const argv[] = {
FUSERMOUNT_PROG,
"-o", opts ? opts : "",
"--",
mountpoint,
NULL,
};
posix_spawn_file_actions_t action;
posix_spawn_file_actions_init(&action);
if (quiet) {
posix_spawn_file_actions_addclose(&action, 1);
posix_spawn_file_actions_addclose(&action, 2);
}
posix_spawn_file_actions_addclose(&action, fds[1]);
int status = posix_spawn(&pid, FUSERMOUNT_DIR "/" FUSERMOUNT_PROG, &action,
NULL, (char *const *) argv, environ)
&& posix_spawnp(&pid, FUSERMOUNT_PROG, &action,
NULL, (char *const *) argv, environ);
posix_spawn_file_actions_destroy(&action);
if(status != 0) {
close(fds[0]);
close(fds[1]);
perror("fuse: posix_spawnp() of fusermount3 failed");
return -1;
}
if(pid == 0) {
char env[10];
const char *argv[32];
int a = 0;
if (quiet) {
int fd = open("/dev/null", O_RDONLY);
if (fd != -1) {
dup2(fd, 1);
dup2(fd, 2);
}
}
argv[a++] = FUSERMOUNT_PROG;
if (opts) {
argv[a++] = "-o";
argv[a++] = opts;
}
argv[a++] = "--";
argv[a++] = mountpoint;
argv[a++] = NULL;
close(fds[1]);
fcntl(fds[0], F_SETFD, 0);
snprintf(env, sizeof(env), "%i", fds[0]);
setenv(FUSE_COMMFD_ENV, env, 1);
exec_fusermount(argv);
perror("fuse: failed to exec fusermount3");
_exit(1);
}
// passed to child now, so can close here.
close(fds[0]);
rv = receive_fd(fds[1]);
int rv = receive_fd(fds[1]);
if (!mo->auto_unmount) {
/* with auto_unmount option fusermount3 will not exit until
util/fusermount.c
+9 -4
View File
@@ -1454,7 +1454,7 @@ int main(int argc, char *argv[])
static int unmount = 0;
static int lazy = 0;
static int quiet = 0;
char *commfd;
char *commfd = NULL;
int cfd;
const char *opts = "";
const char *type = NULL;
@@ -1462,14 +1462,15 @@ int main(int argc, char *argv[])
static const struct option long_opts[] = {
{"unmount", no_argument, NULL, 'u'},
// Note: auto-unmount deliberately does not have a short version.
// It's meant for internal use by mount.c's setup_auto_unmount.
{"auto-unmount", no_argument, NULL, 'U'},
{"lazy", no_argument, NULL, 'z'},
{"quiet", no_argument, NULL, 'q'},
{"help", no_argument, NULL, 'h'},
{"version", no_argument, NULL, 'V'},
{"options", required_argument, NULL, 'o'},
// Note: auto-unmount and comm-fd don't have short versions.
// They'ne meant for internal use by mount.c
{"auto-unmount", no_argument, NULL, 'U'},
{"comm-fd", required_argument, NULL, 'c'},
{0, 0, 0, 0}};
progname = strdup(argc > 0 ? argv[0] : "fusermount");
@@ -1501,6 +1502,9 @@ int main(int argc, char *argv[])
auto_unmount = 1;
setup_auto_unmount_only = 1;
break;
case 'c':
commfd = optarg;
break;
case 'z':
lazy = 1;
break;
@@ -1547,6 +1551,7 @@ int main(int argc, char *argv[])
if (!setup_auto_unmount_only && unmount)
goto do_unmount;
if(commfd == NULL)
commfd = getenv(FUSE_COMMFD_ENV);
if (commfd == NULL) {
fprintf(stderr, "%s: old style mounting not supported\n",