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/* SPDX-License-Identifier: LGPL-2.1-or-later */
#include <fcntl.h>
#include <poll.h>
#include "fd-util.h"
#include "io-util.h"
#include "nscd-flush.h"
#include "socket-util.h"
#include "strv.h"
#include "time-util.h"
#define NSCD_FLUSH_CACHE_TIMEOUT_USEC (5*USEC_PER_SEC)
struct nscdInvalidateRequest {
int32_t version;
int32_t type; /* in glibc this is an enum. We don't replicate this here 1:1. Also, wtf, how unportable is that
* even? */
int32_t key_len;
char dbname[];
};
static int nscd_flush_cache_one(const char *database, usec_t end) {
size_t req_size, has_written = 0, has_read = 0, l;
struct nscdInvalidateRequest *req;
_cleanup_close_ int fd = -EBADF;
int32_t resp;
int events, r;
assert(database);
l = strlen(database);
req_size = offsetof(struct nscdInvalidateRequest, dbname) + l + 1;
req = alloca_safe(req_size);
*req = (struct nscdInvalidateRequest) {
.version = 2,
.type = 10,
.key_len = l + 1,
};
strcpy(req->dbname, database);
fd = socket(AF_UNIX, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
if (fd < 0)
return log_debug_errno(errno, "Failed to allocate nscd socket: %m");
/* Note: connect() returns EINPROGRESS if O_NONBLOCK is set and establishing a connection takes time. The
* kernel lets us know this way that the connection is now being established, and we should watch with poll()
* to learn when it is fully established. That said, AF_UNIX on Linux never triggers this IRL (connect() is
* always instant on AF_UNIX), hence handling this is mostly just an exercise in defensive, protocol-agnostic
* programming.
*
* connect() returns EAGAIN if the socket's backlog limit has been reached. When we see this we give up right
* away, after all this entire function here is written in a defensive style so that a non-responding nscd
* doesn't stall us for good. (Even if we wanted to handle this better: the Linux kernel doesn't really have a
* nice way to connect() to a server synchronously with a time limit that would also cover dealing with the
* backlog limit. After all SO_RCVTIMEO and SR_SNDTIMEO don't apply to connect(), and alarm() is frickin' ugly
* and not really reasonably usable from threads-aware code.) */
r = connect_unix_path(fd, AT_FDCWD, "/run/nscd/socket");
if (r < 0) {
if (r == -EAGAIN)
return log_debug_errno(r, "nscd is overloaded (backlog limit reached) and refuses to take further connections: %m");
if (r != -EINPROGRESS)
return log_debug_errno(r, "Failed to connect to nscd socket: %m");
/* Continue in case of EINPROGRESS, but don't bother with send() or recv() until being notified that
* establishing the connection is complete. */
events = 0;
} else
events = POLLIN|POLLOUT; /* Let's assume initially that we can write and read to the fd, to suppress
* one poll() invocation */
for (;;) {
usec_t p;
if (events & POLLOUT) {
ssize_t m;
assert(has_written < req_size);
m = send(fd, (uint8_t*) req + has_written, req_size - has_written, MSG_NOSIGNAL);
if (m < 0) {
if (errno != EAGAIN) /* Note that EAGAIN is returned by the kernel whenever it can't
* take the data right now, and that includes if the connect() is
* asynchronous and we saw EINPROGRESS on it, and it hasn't
* completed yet. */
return log_debug_errno(errno, "Failed to write to nscd socket: %m");
} else
has_written += m;
}
if (events & (POLLIN|POLLERR|POLLHUP)) {
ssize_t m;
if (has_read >= sizeof(resp))
return log_debug_errno(SYNTHETIC_ERRNO(EIO), "Response from nscd longer than expected: %m");
m = recv(fd, (uint8_t*) &resp + has_read, sizeof(resp) - has_read, 0);
if (m < 0) {
if (errno != EAGAIN)
return log_debug_errno(errno, "Failed to read from nscd socket: %m");
} else if (m == 0) { /* EOF */
if (has_read == 0 && has_written >= req_size) /* Older nscd immediately terminated the
* connection, accept that as OK */
return 1;
return log_debug_errno(SYNTHETIC_ERRNO(EIO), "nscd prematurely ended connection.");
} else
has_read += m;
}
if (has_written >= req_size && has_read >= sizeof(resp)) { /* done? */
if (resp < 0)
return log_debug_errno(SYNTHETIC_ERRNO(EBADMSG), "nscd sent us a negative error number: %i", resp);
if (resp > 0)
return log_debug_errno(resp, "nscd return failure code on invalidating '%s'.", database);
return 1;
}
p = now(CLOCK_MONOTONIC);
if (p >= end)
return -ETIMEDOUT;
events = fd_wait_for_event(fd, POLLIN | (has_written < req_size ? POLLOUT : 0), end - p);
if (events < 0)
return events;
}
}
int nscd_flush_cache(char **databases) {
int r = 0;
/* Tries to invalidate the specified database in nscd. We do this carefully, with a 5s timeout,
* so that we don't block indefinitely on another service. */
usec_t end = usec_add(now(CLOCK_MONOTONIC), NSCD_FLUSH_CACHE_TIMEOUT_USEC);
STRV_FOREACH(i, databases)
RET_GATHER(r, nscd_flush_cache_one(*i, end));
return r;
}
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