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/*
libulockmgr: Userspace Lock Manager Library
Copyright (C) 2006 Miklos Szeredi <miklos@szeredi.hu>
This program can be distributed under the terms of the GNU LGPLv2.
See the file COPYING.LIB
*/
/* #define DEBUG 1 */
#include "ulockmgr.h"
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <pthread.h>
#include <errno.h>
#include <assert.h>
#include <signal.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <sys/wait.h>
struct message {
unsigned intr : 1;
unsigned nofd : 1;
pthread_t thr;
int cmd;
int fd;
struct flock lock;
int error;
};
struct fd_store {
struct fd_store *next;
int fd;
int inuse;
};
struct owner {
struct owner *next;
struct owner *prev;
struct fd_store *fds;
void *id;
size_t id_len;
int cfd;
};
static pthread_mutex_t ulockmgr_lock;
static int ulockmgr_cfd = -1;
static struct owner owner_list = { .next = &owner_list, .prev = &owner_list };
#define MAX_SEND_FDS 2
static void list_del_owner(struct owner *owner)
{
struct owner *prev = owner->prev;
struct owner *next = owner->next;
prev->next = next;
next->prev = prev;
}
static void list_add_owner(struct owner *owner, struct owner *next)
{
struct owner *prev = next->prev;
owner->next = next;
owner->prev = prev;
prev->next = owner;
next->prev = owner;
}
/*
* There's a bug in the linux kernel (< 2.6.22) recv() implementation
* on AF_UNIX, SOCK_STREAM sockets, that could cause it to return
* zero, even if data was available. Retrying the recv will return
* the data in this case.
*/
static int do_recv(int sock, void *buf, size_t len, int flags)
{
int res = recv(sock, buf, len, flags);
if (res == 0)
res = recv(sock, buf, len, flags);
return res;
}
static int ulockmgr_send_message(int sock, void *buf, size_t buflen,
int *fdp, int numfds)
{
struct msghdr msg;
struct cmsghdr *p_cmsg;
struct iovec vec;
size_t cmsgbuf[CMSG_SPACE(sizeof(int) * MAX_SEND_FDS) / sizeof(size_t)];
int res;
assert(numfds <= MAX_SEND_FDS);
msg.msg_control = cmsgbuf;
msg.msg_controllen = sizeof(cmsgbuf);
p_cmsg = CMSG_FIRSTHDR(&msg);
p_cmsg->cmsg_level = SOL_SOCKET;
p_cmsg->cmsg_type = SCM_RIGHTS;
p_cmsg->cmsg_len = CMSG_LEN(sizeof(int) * numfds);
memcpy(CMSG_DATA(p_cmsg), fdp, sizeof(int) * numfds);
msg.msg_controllen = p_cmsg->cmsg_len;
msg.msg_name = NULL;
msg.msg_namelen = 0;
msg.msg_iov = &vec;
msg.msg_iovlen = 1;
msg.msg_flags = 0;
vec.iov_base = buf;
vec.iov_len = buflen;
res = sendmsg(sock, &msg, MSG_NOSIGNAL);
if (res == -1) {
perror("libulockmgr: sendmsg");
return -1;
}
if ((size_t) res != buflen) {
fprintf(stderr, "libulockmgr: sendmsg short\n");
return -1;
}
return 0;
}
static int ulockmgr_start_daemon(void)
{
int sv[2];
int res;
char tmp[64];
res = socketpair(AF_UNIX, SOCK_STREAM, 0, sv);
if (res == -1) {
perror("libulockmgr: socketpair");
return -1;
}
snprintf(tmp, sizeof(tmp), "exec ulockmgr_server %i", sv[0]);
res = system(tmp);
close(sv[0]);
if (res == -1 || !WIFEXITED(res) || WEXITSTATUS(res) != 0) {
close(sv[1]);
return -1;
}
ulockmgr_cfd = sv[1];
return 0;
}
static struct owner *ulockmgr_new_owner(const void *id, size_t id_len)
{
int sv[2];
int res;
char c = 'm';
struct owner *o;
if (ulockmgr_cfd == -1 && ulockmgr_start_daemon() == -1)
return NULL;
o = calloc(1, sizeof(struct owner) + id_len);
if (!o) {
fprintf(stderr, "libulockmgr: failed to allocate memory\n");
return NULL;
}
o->id = o + 1;
o->id_len = id_len;
res = socketpair(AF_UNIX, SOCK_STREAM, 0, sv);
if (res == -1) {
perror("libulockmgr: socketpair");
goto out_free;
}
res = ulockmgr_send_message(ulockmgr_cfd, &c, sizeof(c), &sv[0], 1);
close(sv[0]);
if (res == -1) {
close(ulockmgr_cfd);
ulockmgr_cfd = -1;
goto out_close;
}
o->cfd = sv[1];
memcpy(o->id, id, id_len);
list_add_owner(o, &owner_list);
return o;
out_close:
close(sv[1]);
out_free:
free(o);
return NULL;
}
static int ulockmgr_send_request(struct message *msg, const void *id,
size_t id_len)
{
int sv[2];
int cfd;
struct owner *o;
struct fd_store *f = NULL;
struct fd_store *newf = NULL;
struct fd_store **fp;
int fd = msg->fd;
int cmd = msg->cmd;
int res;
int unlockall = (cmd == F_SETLK && msg->lock.l_type == F_UNLCK &&
msg->lock.l_start == 0 && msg->lock.l_len == 0);
for (o = owner_list.next; o != &owner_list; o = o->next)
if (o->id_len == id_len && memcmp(o->id, id, id_len) == 0)
break;
if (o == &owner_list)
o = NULL;
if (!o && cmd != F_GETLK && msg->lock.l_type != F_UNLCK)
o = ulockmgr_new_owner(id, id_len);
if (!o) {
if (cmd == F_GETLK) {
res = fcntl(msg->fd, F_GETLK, &msg->lock);
return (res == -1) ? -errno : 0;
} else if (msg->lock.l_type == F_UNLCK)
return 0;
else
return -ENOLCK;
}
if (unlockall)
msg->nofd = 1;
else {
for (fp = &o->fds; *fp; fp = &(*fp)->next) {
f = *fp;
if (f->fd == fd) {
msg->nofd = 1;
break;
}
}
}
if (!msg->nofd) {
newf = f = calloc(1, sizeof(struct fd_store));
if (!f) {
fprintf(stderr, "libulockmgr: failed to allocate memory\n");
return -ENOLCK;
}
}
res = socketpair(AF_UNIX, SOCK_STREAM, 0, sv);
if (res == -1) {
perror("libulockmgr: socketpair");
free(newf);
return -ENOLCK;
}
cfd = sv[1];
sv[1] = msg->fd;
res = ulockmgr_send_message(o->cfd, msg, sizeof(struct message), sv,
msg->nofd ? 1 : 2);
close(sv[0]);
if (res == -1) {
free(newf);
close(cfd);
return -EIO;
}
if (newf) {
newf->fd = msg->fd;
newf->next = o->fds;
o->fds = newf;
}
if (f)
f->inuse++;
res = do_recv(cfd, msg, sizeof(struct message), MSG_WAITALL);
if (res == -1) {
perror("libulockmgr: recv");
msg->error = EIO;
} else if (res != sizeof(struct message)) {
fprintf(stderr, "libulockmgr: recv short\n");
msg->error = EIO;
} else if (cmd == F_SETLKW && msg->error == EAGAIN) {
pthread_mutex_unlock(&ulockmgr_lock);
while (1) {
sigset_t old;
sigset_t unblock;
int errno_save;
sigemptyset(&unblock);
sigaddset(&unblock, SIGUSR1);
pthread_sigmask(SIG_UNBLOCK, &unblock, &old);
res = do_recv(cfd, msg, sizeof(struct message),
MSG_WAITALL);
errno_save = errno;
pthread_sigmask(SIG_SETMASK, &old, NULL);
if (res == sizeof(struct message))
break;
else if (res >= 0) {
fprintf(stderr, "libulockmgr: recv short\n");
msg->error = EIO;
break;
} else if (errno_save != EINTR) {
errno = errno_save;
perror("libulockmgr: recv");
msg->error = EIO;
break;
}
msg->intr = 1;
res = send(o->cfd, msg, sizeof(struct message),
MSG_NOSIGNAL);
if (res == -1) {
perror("libulockmgr: send");
msg->error = EIO;
break;
}
if (res != sizeof(struct message)) {
fprintf(stderr, "libulockmgr: send short\n");
msg->error = EIO;
break;
}
}
pthread_mutex_lock(&ulockmgr_lock);
}
if (f)
f->inuse--;
close(cfd);
if (unlockall) {
for (fp = &o->fds; *fp;) {
f = *fp;
if (f->fd == fd && !f->inuse) {
*fp = f->next;
free(f);
} else
fp = &f->next;
}
if (!o->fds) {
list_del_owner(o);
close(o->cfd);
free(o);
}
/* Force OK on unlock-all, since it _will_ succeed once the
owner is deleted */
msg->error = 0;
}
return -msg->error;
}
#ifdef DEBUG
static uint32_t owner_hash(const unsigned char *id, size_t id_len)
{
uint32_t h = 0;
size_t i;
for (i = 0; i < id_len; i++)
h = ((h << 8) | (h >> 24)) ^ id[i];
return h;
}
#endif
static int ulockmgr_canonicalize(int fd, struct flock *lock)
{
off_t offset;
if (lock->l_whence == SEEK_CUR) {
offset = lseek(fd, 0, SEEK_CUR);
if (offset == (off_t) -1)
return -errno;
} else if (lock->l_whence == SEEK_END) {
struct stat stbuf;
int res = fstat(fd, &stbuf);
if (res == -1)
return -errno;
offset = stbuf.st_size;
} else
offset = 0;
lock->l_whence = SEEK_SET;
lock->l_start += offset;
if (lock->l_start < 0)
return -EINVAL;
if (lock->l_len < 0) {
lock->l_start += lock->l_len;
if (lock->l_start < 0)
return -EINVAL;
lock->l_len = -lock->l_len;
}
if (lock->l_len && lock->l_start + lock->l_len - 1 < 0)
return -EINVAL;
return 0;
}
int ulockmgr_op(int fd, int cmd, struct flock *lock, const void *owner,
size_t owner_len)
{
int err;
struct message msg;
sigset_t old;
sigset_t block;
if (cmd != F_GETLK && cmd != F_SETLK && cmd != F_SETLKW)
return -EINVAL;
if (lock->l_type != F_RDLCK && lock->l_type != F_WRLCK &&
lock->l_type != F_UNLCK)
return -EINVAL;
if (lock->l_whence != SEEK_SET && lock->l_whence != SEEK_CUR &&
lock->l_whence != SEEK_END)
return -EINVAL;
#ifdef DEBUG
fprintf(stderr, "libulockmgr: %i %i %i %lli %lli own: 0x%08x\n",
cmd, lock->l_type, lock->l_whence, lock->l_start, lock->l_len,
owner_hash(owner, owner_len));
#endif
/* Unlock should never block anyway */
if (cmd == F_SETLKW && lock->l_type == F_UNLCK)
cmd = F_SETLK;
memset(&msg, 0, sizeof(struct message));
msg.cmd = cmd;
msg.fd = fd;
msg.lock = *lock;
err = ulockmgr_canonicalize(fd, &msg.lock);
if (err)
return err;
sigemptyset(&block);
sigaddset(&block, SIGUSR1);
pthread_sigmask(SIG_BLOCK, &block, &old);
pthread_mutex_lock(&ulockmgr_lock);
err = ulockmgr_send_request(&msg, owner, owner_len);
pthread_mutex_unlock(&ulockmgr_lock);
pthread_sigmask(SIG_SETMASK, &old, NULL);
if (!err && cmd == F_GETLK) {
if (msg.lock.l_type == F_UNLCK)
lock->l_type = F_UNLCK;
else
*lock = msg.lock;
}
return err;
}