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use poll() instead of select() when possible #705

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use poll() instead of select() when possible #705

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3180afc
use poll() instead of select() when possible; fail select with EBADF …
2128506 Jul 3, 2023
adad266
fixed handling of infinite timeout in select/poll
2128506 Jul 3, 2023
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3 changes: 2 additions & 1 deletion configure.ac
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Original file line number Diff line number Diff line change
Expand Up @@ -86,6 +86,7 @@ AC_CHECK_HEADERS([ \
netdb.h \
netinet/in.h \
netinet/tcp.h \
poll.h \
sys/ioctl.h \
sys/params.h \
sys/socket.h \
Expand All @@ -104,7 +105,7 @@ AC_CHECK_DECLS([__CYGWIN__])
AC_SEARCH_LIBS(accept, network socket)

# Checks for library functions.
AC_CHECK_FUNCS([accept4 getaddrinfo gettimeofday inet_pton inet_ntop select socket strerror strlcpy])
AC_CHECK_FUNCS([accept4 getaddrinfo gettimeofday inet_pton inet_ntop poll select socket strerror strlcpy])

# Required for MinGW with GCC v4.8.1 on Win7
AC_DEFINE(WINVER, 0x0501, _)
Expand Down
2 changes: 1 addition & 1 deletion src/modbus-private.h
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Original file line number Diff line number Diff line change
Expand Up @@ -89,7 +89,7 @@ typedef struct _modbus_backend {
unsigned int (*is_connected)(modbus_t *ctx);
void (*close)(modbus_t *ctx);
int (*flush)(modbus_t *ctx);
int (*select)(modbus_t *ctx, fd_set *rset, struct timeval *tv, int msg_length);
int (*select)(modbus_t *ctx, struct timeval *tv, int msg_length);
void (*free)(modbus_t *ctx);
} modbus_backend_t;

Expand Down
40 changes: 36 additions & 4 deletions src/modbus-rtu.c
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Original file line number Diff line number Diff line change
Expand Up @@ -12,6 +12,9 @@
#ifndef _MSC_VER
#include <unistd.h>
#endif
#if HAVE_POLL_H
#include <poll.h>
#endif
#include "modbus-private.h"
#include <assert.h>

Expand Down Expand Up @@ -1130,7 +1133,7 @@ static int _modbus_rtu_flush(modbus_t *ctx)
}

static int
_modbus_rtu_select(modbus_t *ctx, fd_set *rset, struct timeval *tv, int length_to_read)
_modbus_rtu_select(modbus_t *ctx, struct timeval *tv, int length_to_read)
{
int s_rc;
#if defined(_WIN32)
Expand All @@ -1144,19 +1147,48 @@ _modbus_rtu_select(modbus_t *ctx, fd_set *rset, struct timeval *tv, int length_t
if (s_rc < 0) {
return -1;
}

#else
while ((s_rc = select(ctx->s + 1, rset, NULL, NULL, tv)) == -1) {
#if HAVE_POLL
struct pollfd fds;
fds.fd = ctx->s;
fds.events = POLLIN;
fds.revents = 0;
while ((s_rc = poll(&fds, 1, (tv != NULL) ? tv->tv_sec * 1000 + tv->tv_usec / 1000 : -1)) == -1) {
if (errno == EINTR) {
if (ctx->debug) {
fprintf(stderr, "A non blocked signal was caught\n");
}
} else if (errno != EAGAIN) {
return -1;
}
}
#else
fd_set rset;

if (ctx->s >= FD_SETSIZE) {
if (ctx->debug) {
fprintf(stderr, "File descriptor greater than FD_SETSIZE passed to select() call\n");
}
errno = EBADF;
return -1;
}

FD_ZERO(&rset);
FD_SET(ctx->s, &rset);
while ((s_rc = select(ctx->s + 1, &rset, NULL, NULL, tv)) == -1) {
if (errno == EINTR) {
if (ctx->debug) {
fprintf(stderr, "A non blocked signal was caught\n");
}
/* Necessary after an error */
FD_ZERO(rset);
FD_SET(ctx->s, rset);
FD_ZERO(&rset);
FD_SET(ctx->s, &rset);
} else {
return -1;
}
}
#endif

if (s_rc == 0) {
/* Timeout */
Expand Down
57 changes: 52 additions & 5 deletions src/modbus-tcp.c
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Original file line number Diff line number Diff line change
Expand Up @@ -24,6 +24,10 @@
#include <signal.h>
#include <sys/types.h>

#if HAVE_POLL_H
#include <poll.h>
#endif

#if defined(_WIN32)
/* Already set in modbus-tcp.h but it seems order matters in VS2005 */
# include <winsock2.h>
Expand Down Expand Up @@ -284,15 +288,30 @@ static int _connect(int sockfd,
#else
if (rc == -1 && errno == EINPROGRESS) {
#endif
fd_set wset;
int optval;
socklen_t optlen = sizeof(optval);
#if HAVE_POLL
struct pollfd fds;

/* Wait to be available in writing */
fds.fd = sockfd;
fds.events = POLLOUT;
fds.revents = 0;
rc = poll(&fds, 1, (ro_tv != NULL) ? ro_tv->tv_sec * 1000 + ro_tv->tv_usec / 1000 : -1);
#else
fd_set wset;
struct timeval tv = *ro_tv;

if (sockfd >= FD_SETSIZE) {
errno = EBADF;
return -1;
}

/* Wait to be available in writing */
FD_ZERO(&wset);
FD_SET(sockfd, &wset);
rc = select(sockfd + 1, NULL, &wset, NULL, &tv);
#endif
if (rc <= 0) {
/* Timeout or fail */
return -1;
Expand Down Expand Up @@ -759,21 +778,49 @@ int modbus_tcp_pi_accept(modbus_t *ctx, int *s)
}

static int
_modbus_tcp_select(modbus_t *ctx, fd_set *rset, struct timeval *tv, int length_to_read)
_modbus_tcp_select(modbus_t *ctx, struct timeval *tv, int length_to_read)
{
int s_rc;
while ((s_rc = select(ctx->s + 1, rset, NULL, NULL, tv)) == -1) {
#if HAVE_POLL
struct pollfd fds;
fds.fd = ctx->s;
fds.events = POLLIN;
fds.revents = 0;
while ((s_rc = poll(&fds, 1, (tv != NULL) ? tv->tv_sec * 1000 + tv->tv_usec / 1000 : -1)) == -1) {
if (errno == EINTR) {
if (ctx->debug) {
fprintf(stderr, "A non blocked signal was caught\n");
}
} else if (errno != EAGAIN) {
return -1;
}
}
#else
fd_set rset;

if (ctx->s >= FD_SETSIZE) {
if (ctx->debug) {
fprintf(stderr, "File descriptor greater than FD_SETSIZE passed to select() call\n");
}
errno = EBADF;
return -1;
}

FD_ZERO(&rset);
FD_SET(ctx->s, &rset);
while ((s_rc = select(ctx->s + 1, &rset, NULL, NULL, tv)) == -1) {
if (errno == EINTR) {
if (ctx->debug) {
fprintf(stderr, "A non blocked signal was caught\n");
}
/* Necessary after an error */
FD_ZERO(rset);
FD_SET(ctx->s, rset);
FD_ZERO(&rset);
FD_SET(ctx->s, &rset);
} else {
return -1;
}
}
#endif

if (s_rc == 0) {
errno = ETIMEDOUT;
Expand Down
7 changes: 1 addition & 6 deletions src/modbus.c
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Expand Up @@ -350,7 +350,6 @@ compute_data_length_after_meta(modbus_t *ctx, uint8_t *msg, msg_type_t msg_type)
int _modbus_receive_msg(modbus_t *ctx, uint8_t *msg, msg_type_t msg_type)
{
int rc;
fd_set rset;
struct timeval tv;
struct timeval *p_tv;
unsigned int length_to_read;
Expand All @@ -375,10 +374,6 @@ int _modbus_receive_msg(modbus_t *ctx, uint8_t *msg, msg_type_t msg_type)
return -1;
}

/* Add a file descriptor to the set */
FD_ZERO(&rset);
FD_SET(ctx->s, &rset);

/* We need to analyse the message step by step. At the first step, we want
* to reach the function code because all packets contain this
* information. */
Expand All @@ -405,7 +400,7 @@ int _modbus_receive_msg(modbus_t *ctx, uint8_t *msg, msg_type_t msg_type)
}

while (length_to_read != 0) {
rc = ctx->backend->select(ctx, &rset, p_tv, length_to_read);
rc = ctx->backend->select(ctx, p_tv, length_to_read);
if (rc == -1) {
_error_print(ctx, "select");
if (ctx->error_recovery & MODBUS_ERROR_RECOVERY_LINK) {
Expand Down