[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] [PATCH 02/13] libxenstore: Provide xs_check_watch
Event-driven programs want to wait until the xs_fileno triggers for reading, and then repeatedly call xs_check_watch. Also xs_read_watch exposes a useless "num" out parameter, which should always (if things aren't going hideously wrong) be at least 2 and which the caller shouldn't be interested in. So xs_check_watch doesn't have one of those. Signed-off-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx> --- tools/xenstore/xs.c | 89 ++++++++++++++++++++++++++++++++++++++++++++------- tools/xenstore/xs.h | 16 +++++++++ 2 files changed, 93 insertions(+), 12 deletions(-) diff --git a/tools/xenstore/xs.c b/tools/xenstore/xs.c index c72ea83..5d0b567 100644 --- a/tools/xenstore/xs.c +++ b/tools/xenstore/xs.c @@ -132,7 +132,23 @@ struct xs_handle { #endif -static int read_message(struct xs_handle *h); +static int read_message(struct xs_handle *h, int nonblocking); + +static void setnonblock(int fd, int nonblock) { + int esave = errno; + int flags = fcntl(fd, F_GETFL); + if (flags == -1) + goto out; + + if (nonblock) + flags |= O_NONBLOCK; + else + flags &= ~O_NONBLOCK; + + fcntl(fd, F_SETFL, flags); +out: + errno = esave; +} int xs_fileno(struct xs_handle *h) { @@ -327,8 +343,16 @@ void xs_close(struct xs_handle* xsh) xs_daemon_close(xsh); } -static bool read_all(int fd, void *data, unsigned int len) +static bool read_all(int fd, void *data, unsigned int len, int nonblocking) + /* With nonblocking, either reads either everything requested, + * or nothing. */ { + if (!len) + return true; + + if (nonblocking) + setnonblock(fd, 1); + while (len) { int done; @@ -336,18 +360,28 @@ static bool read_all(int fd, void *data, unsigned int len) if (done < 0) { if (errno == EINTR) continue; - return false; + goto out_false; } if (done == 0) { /* It closed fd on us? EBADF is appropriate. */ errno = EBADF; - return false; + goto out_false; } data += done; len -= done; + + if (nonblocking) { + setnonblock(fd, 0); + nonblocking = 0; + } } return true; + +out_false: + if (nonblocking) + setnonblock(fd, 0); + return false; } #ifdef XSTEST @@ -376,7 +410,7 @@ static void *read_reply( read_from_thread = read_thread_exists(h); /* Read from comms channel ourselves if there is no reader thread. */ - if (!read_from_thread && (read_message(h) == -1)) + if (!read_from_thread && (read_message(h, 0) == -1)) return NULL; mutex_lock(&h->reply_mutex); @@ -695,7 +729,8 @@ bool xs_watch(struct xs_handle *h, const char *path, const char *token) * Returns array of two pointers: path and token, or NULL. * Call free() after use. */ -char **xs_read_watch(struct xs_handle *h, unsigned int *num) +static char **read_watch_internal(struct xs_handle *h, unsigned int *num, + int nonblocking) { struct xs_stored_msg *msg; char **ret, *strings, c = 0; @@ -709,14 +744,20 @@ char **xs_read_watch(struct xs_handle *h, unsigned int *num) * we haven't called xs_watch. Presumably the application * will do so later; in the meantime we just block. */ - while (list_empty(&h->watch_list) && h->fd != -1) + while (list_empty(&h->watch_list) && h->fd != -1) { + if (nonblocking) { + mutex_unlock(&h->watch_mutex); + errno = EAGAIN; + return 0; + } condvar_wait(&h->watch_condvar, &h->watch_mutex); + } #else /* !defined(USE_PTHREAD) */ /* Read from comms channel ourselves if there are no threads * and therefore no reader thread. */ assert(!read_thread_exists(h)); /* not threadsafe but worth a check */ - if ((read_message(h) == -1)) + if ((read_message(h, nonblocking) == -1)) return NULL; #endif /* !defined(USE_PTHREAD) */ @@ -762,6 +803,24 @@ char **xs_read_watch(struct xs_handle *h, unsigned int *num) return ret; } +char **xs_check_watch(struct xs_handle *h) +{ + unsigned int num; + char **ret; + ret = read_watch_internal(h, &num, 1); + if (ret) assert(num >= 2); + return ret; +} + +/* Find out what node change was on (will block if nothing pending). + * Returns array of two pointers: path and token, or NULL. + * Call free() after use. + */ +char **xs_read_watch(struct xs_handle *h, unsigned int *num) +{ + return read_watch_internal(h, num, 0); +} + /* Remove a watch on a node. * Returns false on failure (no watch on that node). */ @@ -942,11 +1001,17 @@ char *xs_debug_command(struct xs_handle *h, const char *cmd, ARRAY_SIZE(iov), NULL); } -static int read_message(struct xs_handle *h) +static int read_message(struct xs_handle *h, int nonblocking) { /* IMPORTANT: It is forbidden to call this function without * acquiring the request lock and checking that h->read_thr_exists * is false. See "Lock discipline" in struct xs_handle, above. */ + + /* If nonblocking==1, this function will always read either + * nothing, returning -1 and setting errno==EAGAIN, or we read + * whole amount requested. Ie as soon as we have the start of + * the message we block until we get all of it. + */ struct xs_stored_msg *msg = NULL; char *body = NULL; @@ -958,7 +1023,7 @@ static int read_message(struct xs_handle *h) if (msg == NULL) goto error; cleanup_push(free, msg); - if (!read_all(h->fd, &msg->hdr, sizeof(msg->hdr))) { /* Cancellation point */ + if (!read_all(h->fd, &msg->hdr, sizeof(msg->hdr), nonblocking)) { /* Cancellation point */ saved_errno = errno; goto error_freemsg; } @@ -968,7 +1033,7 @@ static int read_message(struct xs_handle *h) if (body == NULL) goto error_freemsg; cleanup_push(free, body); - if (!read_all(h->fd, body, msg->hdr.len)) { /* Cancellation point */ + if (!read_all(h->fd, body, msg->hdr.len, 0)) { /* Cancellation point */ saved_errno = errno; goto error_freebody; } @@ -1023,7 +1088,7 @@ static void *read_thread(void *arg) struct xs_handle *h = arg; int fd; - while (read_message(h) != -1) + while (read_message(h, 0) != -1) continue; /* An error return from read_message leaves the socket in an undefined diff --git a/tools/xenstore/xs.h b/tools/xenstore/xs.h index 1cbe255..63f535d 100644 --- a/tools/xenstore/xs.h +++ b/tools/xenstore/xs.h @@ -135,6 +135,22 @@ bool xs_watch(struct xs_handle *h, const char *path, const char *token); /* Return the FD to poll on to see if a watch has fired. */ int xs_fileno(struct xs_handle *h); +/* Check for node changes. On success, returns a non-NULL pointer ret + * such that ret[0] and ret[1] are valid C strings, namely the + * triggering path (see docs/misc/xenstore.txt) and the token (from + * xs_watch). On error return value is NULL setting errno. + * + * Callers should, after xs_fileno has become readable, repeatedly + * call xs_check_watch until it returns NULL and sets errno to EAGAIN. + * (If the fd became readable, xs_check_watch is allowed to make it no + * longer show up as readable even if future calls to xs_check_watch + * will return more watch events.) + * + * After the caller is finished with the returned information it + * should be freed all in one go with free(ret). + */ +char **xs_check_watch(struct xs_handle *h); + /* Find out what node change was on (will block if nothing pending). * Returns array containing the path and token. Use XS_WATCH_* to access these * elements. Call free() after use. -- 1.7.2.5 _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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