Mailing List Archive

In Linux select() typically supports up to 1024 file descriptors. This can be
a problem when user tries to boot up many guests. Switching to poll() has
minimum impact on existing code and has better scalibility.

pollfd array is dynamically allocated / reallocated. If the array fails to
expand, we just ignore the incoming fd.

Change from V2:
* remove unnecessary malloc in initialize_pollfd_arrays
* use ROUND_UP to get new size of arrays

Change from V3:
* remove initialize and destroy function for array
* embedded tracking structure in struct domain, eliminate fd_to_pollfd

Change from V4:
* make xs_pollfd local to io.c
* add back the 5 ms fuzz
* handle POLLERR and POLLHUP
* treat POLLPRI as error if set in revents
* abort if xenconsoled's own fds get screwed
* handle broken tty if tty's fds get screwed

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
---
tools/console/daemon/io.c | 189 +++++++++++++++++++++++++++++++--------------
1 file changed, 131 insertions(+), 58 deletions(-)

diff --git a/tools/console/daemon/io.c b/tools/console/daemon/io.c
index 48fe151..8d16cac 100644
--- a/tools/console/daemon/io.c
+++ b/tools/console/daemon/io.c
@@ -28,7 +28,7 @@
#include <stdlib.h>
#include <errno.h>
#include <string.h>
-#include <sys/select.h>
+#include <poll.h>
#include <fcntl.h>
#include <unistd.h>
#include <termios.h>
@@ -69,6 +69,7 @@ static int log_hv_fd = -1;
static evtchn_port_or_error_t log_hv_evtchn = -1;
static xc_interface *xch; /* why does xenconsoled have two xc handles ? */
static xc_evtchn *xce_handle = NULL;
+static struct pollfd *xce_pollfd = NULL;

struct buffer {
char *data;
@@ -81,7 +82,9 @@ struct buffer {
struct domain {
int domid;
int master_fd;
+ struct pollfd *master_pollfd;
int slave_fd;
+ struct pollfd *slave_pollfd;
int log_fd;
bool is_dead;
unsigned last_seen;
@@ -92,6 +95,7 @@ struct domain {
evtchn_port_or_error_t local_port;
evtchn_port_or_error_t remote_port;
xc_evtchn *xce_handle;
+ struct pollfd *xce_pollfd;
struct xencons_interface *interface;
int event_count;
long long next_period;
@@ -769,6 +773,17 @@ static int ring_free_bytes(struct domain *dom)
return (sizeof(intf->in) - space);
}

+static void domain_handle_broken_tty(struct domain *dom, int recreate)
+{
+ domain_close_tty(dom);
+
+ if (recreate) {
+ domain_create_tty(dom);
+ } else {
+ shutdown_domain(dom);
+ }
+}
+
static void handle_tty_read(struct domain *dom)
{
ssize_t len = 0;
@@ -794,13 +809,7 @@ static void handle_tty_read(struct domain *dom)
* keep the slave open for the duration.
*/
if (len < 0) {
- domain_close_tty(dom);
-
- if (domain_is_valid(dom->domid)) {
- domain_create_tty(dom);
- } else {
- shutdown_domain(dom);
- }
+ domain_handle_broken_tty(dom, domain_is_valid(dom->domid));
} else if (domain_is_valid(dom->domid)) {
prod = intf->in_prod;
for (i = 0; i < len; i++) {
@@ -828,14 +837,7 @@ static void handle_tty_write(struct domain *dom)
if (len < 1) {
dolog(LOG_DEBUG, "Write failed on domain %d: %zd, %d\n",
dom->domid, len, errno);
-
- domain_close_tty(dom);
-
- if (domain_is_valid(dom->domid)) {
- domain_create_tty(dom);
- } else {
- shutdown_domain(dom);
- }
+ domain_handle_broken_tty(dom, domain_is_valid(dom->domid));
} else {
buffer_advance(&dom->buffer, len);
}
@@ -928,9 +930,53 @@ static void handle_log_reload(void)
}
}

+struct pollfd *xs_pollfd;
+static struct pollfd *fds;
+static unsigned int current_array_size;
+static unsigned int nr_fds;
+
+#define ROUNDUP(_x,_w) (((unsigned long)(_x)+(1UL<<(_w))-1) & ~((1UL<<(_w))-1))
+static struct pollfd *set_fds(int fd, short events)
+{
+ struct pollfd *ret;
+ if (current_array_size < nr_fds + 1) {
+ struct pollfd *new_fds = NULL;
+ unsigned long newsize;
+
+ /* Round up to 2^8 boundary, in practice this just
+ * make newsize larger than current_array_size.
+ */
+ newsize = ROUNDUP(nr_fds + 1, 8);
+
+ new_fds = realloc(fds, sizeof(struct pollfd)*newsize);
+ if (!new_fds)
+ goto fail;
+ fds = new_fds;
+
+ memset(&fds[0] + current_array_size, 0,
+ sizeof(struct pollfd) * (newsize-current_array_size));
+ current_array_size = newsize;
+ }
+
+ fds[nr_fds].fd = fd;
+ fds[nr_fds].events = events;
+ ret = &fds[nr_fds];
+ nr_fds++;
+
+ return ret;
+fail:
+ dolog(LOG_ERR, "realloc failed, ignoring fd %d\n", fd);
+ return NULL;
+}
+
+static void reset_fds(void)
+{
+ nr_fds = 0;
+ memset(fds, 0, sizeof(struct pollfd) * current_array_size);
+}
+
void handle_io(void)
{
- fd_set readfds, writefds;
int ret;

if (log_hv) {
@@ -959,21 +1005,17 @@ void handle_io(void)

for (;;) {
struct domain *d, *n;
- int max_fd = -1;
- struct timeval timeout;
+ int poll_timeout; /* timeout in milliseconds */
struct timespec ts;
long long now, next_timeout = 0;

- FD_ZERO(&readfds);
- FD_ZERO(&writefds);
+ reset_fds();

- FD_SET(xs_fileno(xs), &readfds);
- max_fd = MAX(xs_fileno(xs), max_fd);
+ xs_pollfd = set_fds(xs_fileno(xs), POLLIN|POLLPRI);

- if (log_hv) {
- FD_SET(xc_evtchn_fd(xce_handle), &readfds);
- max_fd = MAX(xc_evtchn_fd(xce_handle), max_fd);
- }
+ if (log_hv)
+ xce_pollfd = set_fds(xc_evtchn_fd(xce_handle),
+ POLLIN|POLLPRI);

if (clock_gettime(CLOCK_MONOTONIC, &ts) < 0)
return;
@@ -982,10 +1024,12 @@ void handle_io(void)
/* Re-calculate any event counter allowances & unblock
domains with new allowance */
for (d = dom_head; d; d = d->next) {
- /* Add 5ms of fuzz since select() often returns
- a couple of ms sooner than requested. Without
- the fuzz we typically do an extra spin in select()
- with a 1/2 ms timeout every other iteration */
+ /* CS 16257:955ee4fa1345 introduces a 5ms fuzz
+ * for select(), it is not clear poll() has
+ * similar behavior (returning a couple of ms
+ * sooner than requested) as well. Just leave
+ * the fuzz here. Remove it with a separate
+ * patch if necessary */
if ((now+5) > d->next_period) {
d->next_period = now + RATE_LIMIT_PERIOD;
if (d->event_count >= RATE_LIMIT_ALLOWANCE) {
@@ -1006,75 +1050,101 @@ void handle_io(void)
!d->buffer.max_capacity ||
d->buffer.size < d->buffer.max_capacity) {
int evtchn_fd = xc_evtchn_fd(d->xce_handle);
- FD_SET(evtchn_fd, &readfds);
- max_fd = MAX(evtchn_fd, max_fd);
+ d->xce_pollfd = set_fds(evtchn_fd,
+ POLLIN|POLLPRI);
}
}

if (d->master_fd != -1) {
+ short events = 0;
if (!d->is_dead && ring_free_bytes(d))
- FD_SET(d->master_fd, &readfds);
+ events |= POLLIN;

if (!buffer_empty(&d->buffer))
- FD_SET(d->master_fd, &writefds);
- max_fd = MAX(d->master_fd, max_fd);
+ events |= POLLOUT;
+
+ if (events)
+ d->master_pollfd =
+ set_fds(d->master_fd,
+ events|POLLPRI);
}
}

/* If any domain has been rate limited, we need to work
- out what timeout to supply to select */
+ out what timeout to supply to poll */
if (next_timeout) {
long long duration = (next_timeout - now);
if (duration <= 0) /* sanity check */
duration = 1;
- timeout.tv_sec = duration / 1000;
- timeout.tv_usec = ((duration - (timeout.tv_sec * 1000))
- * 1000);
+ poll_timeout = (int)duration;
}

- ret = select(max_fd + 1, &readfds, &writefds, 0,
- next_timeout ? &timeout : NULL);
+ ret = poll(fds, nr_fds, next_timeout ? poll_timeout : -1);

if (log_reload) {
handle_log_reload();
log_reload = 0;
}

- /* Abort if select failed, except for EINTR cases
+ /* Abort if poll failed, except for EINTR cases
which indicate a possible log reload */
if (ret == -1) {
if (errno == EINTR)
continue;
- dolog(LOG_ERR, "Failure in select: %d (%s)",
+ dolog(LOG_ERR, "Failure in poll: %d (%s)",
errno, strerror(errno));
break;
}

- if (log_hv && FD_ISSET(xc_evtchn_fd(xce_handle), &readfds))
- handle_hv_logs();
+ if (log_hv && xce_pollfd) {
+ if (xce_pollfd->revents & ~(POLLIN|POLLOUT|POLLPRI)) {
+ dolog(LOG_ERR,
+ "Failure in poll xce_handle: %d (%s)",
+ errno, strerror(errno));
+ break;
+ } else if (xce_pollfd->revents & POLLIN)
+ handle_hv_logs();
+ }

if (ret <= 0)
continue;

- if (FD_ISSET(xs_fileno(xs), &readfds))
- handle_xs();
+ if (xs_pollfd) {
+ if (xs_pollfd->revents & ~(POLLIN|POLLOUT|POLLPRI)) {
+ dolog(LOG_ERR,
+ "Failure in poll xs_handle: %d (%s)",
+ errno, strerror(errno));
+ break;
+ } else if (xs_pollfd->revents & POLLIN)
+ handle_xs();
+ }

for (d = dom_head; d; d = n) {
n = d->next;
if (d->event_count < RATE_LIMIT_ALLOWANCE) {
if (d->xce_handle != NULL &&
- FD_ISSET(xc_evtchn_fd(d->xce_handle),
- &readfds))
- handle_ring_read(d);
+ d->xce_pollfd &&
+ !(d->xce_pollfd->revents &
+ ~(POLLIN|POLLOUT|POLLPRI)) &&
+ (d->xce_pollfd->revents &
+ POLLIN))
+ handle_ring_read(d);
}

- if (d->master_fd != -1 && FD_ISSET(d->master_fd,
- &readfds))
- handle_tty_read(d);
-
- if (d->master_fd != -1 && FD_ISSET(d->master_fd,
- &writefds))
- handle_tty_write(d);
+ if (d->master_fd != -1 && d->master_pollfd) {
+ if (d->master_pollfd->revents &
+ ~(POLLIN|POLLOUT|POLLPRI))
+ domain_handle_broken_tty(d,
+ domain_is_valid(d->domid));
+ else {
+ if (d->master_pollfd->revents &
+ POLLIN)
+ handle_tty_read(d);
+ if (d->master_pollfd->revents &
+ POLLOUT)
+ handle_tty_write(d);
+ }
+ }

if (d->last_seen != enum_pass)
shutdown_domain(d);
@@ -1084,6 +1154,9 @@ void handle_io(void)
}
}

+ free(fds);
+ current_array_size = 0;
+
out:
if (log_hv_fd != -1) {
close(log_hv_fd);
--
1.7.10.4


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