[lttng-dev] [PATCH lttng-tools] Add wrappers for pipe

David Goulet dgoulet at efficios.com
Fri May 10 12:09:31 EDT 2013


This is to help use pipes in a way where partial read/write and EINTR
are handled in one single call site.

Two new files are created, pipe.c/.h which are part of libcommon. The
open, close, read and write calls are implemented using a custom
lttng_pipe data structure and protected by operation's mutex. A destroy
function is also available to cleanup memory once done with a pipe.

Signed-off-by: David Goulet <dgoulet at efficios.com>
---
 src/common/Makefile.am |    3 +-
 src/common/pipe.c      |  252 ++++++++++++++++++++++++++++++++++++++++++++++++
 src/common/pipe.h      |   62 ++++++++++++
 3 files changed, 316 insertions(+), 1 deletion(-)
 create mode 100644 src/common/pipe.c
 create mode 100644 src/common/pipe.h

diff --git a/src/common/Makefile.am b/src/common/Makefile.am
index f2ea40a..6ba6c2b 100644
--- a/src/common/Makefile.am
+++ b/src/common/Makefile.am
@@ -13,7 +13,8 @@ noinst_HEADERS = lttng-kernel.h defaults.h macros.h error.h futex.h \
 noinst_LTLIBRARIES = libcommon.la
 
 libcommon_la_SOURCES = error.h error.c utils.c utils.h runas.c runas.h \
-                       common.h futex.c futex.h uri.c uri.h defaults.c
+                       common.h futex.c futex.h uri.c uri.h defaults.c \
+                       pipe.c pipe.h
 libcommon_la_LIBADD = -luuid
 
 # Consumer library
diff --git a/src/common/pipe.c b/src/common/pipe.c
new file mode 100644
index 0000000..89853da
--- /dev/null
+++ b/src/common/pipe.c
@@ -0,0 +1,252 @@
+/*
+ * Copyright (C) 2013 - David Goulet <dgoulet at efficios.com>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License, version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program; if not, write to the Free Software Foundation, Inc., 51
+ * Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#define _GNU_SOURCE
+#include <assert.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+#include <common/common.h>
+
+#include "pipe.h"
+
+/*
+ * Lock read side of a pipe.
+ */
+static void lock_read_side(struct lttng_pipe *pipe)
+{
+	pthread_mutex_lock(&pipe->read_mutex);
+}
+
+/*
+ * Unlock read side of a pipe.
+ */
+static void unlock_read_side(struct lttng_pipe *pipe)
+{
+	pthread_mutex_unlock(&pipe->read_mutex);
+}
+
+/*
+ * Lock write side of a pipe.
+ */
+static void lock_write_side(struct lttng_pipe *pipe)
+{
+	pthread_mutex_lock(&pipe->write_mutex);
+}
+
+/*
+ * Unlock write side of a pipe.
+ */
+static void unlock_write_side(struct lttng_pipe *pipe)
+{
+	pthread_mutex_unlock(&pipe->write_mutex);
+}
+
+/*
+ * Open a new lttng pipe and set flags using fcntl().
+ *
+ * Return a newly allocated lttng pipe on success or else NULL.
+ */
+struct lttng_pipe *lttng_pipe_open(int flags)
+{
+	int ret;
+	struct lttng_pipe *p;
+
+	p = zmalloc(sizeof(*p));
+	if (!p) {
+		PERROR("zmalloc pipe open");
+		goto error;
+	}
+
+	ret = pipe(p->fd);
+	if (ret < 0) {
+		PERROR("lttng pipe");
+		goto error;
+	}
+
+	if (flags) {
+		int i;
+
+		for (i = 0; i < 2; i++) {
+			ret = fcntl(p->fd[i], F_SETFD, flags);
+			if (ret < 0) {
+				PERROR("fcntl lttng pipe %d", flags);
+				goto error;
+			}
+		}
+	}
+
+	pthread_mutex_init(&p->read_mutex, NULL);
+	pthread_mutex_init(&p->write_mutex, NULL);
+	p->r_state = LTTNG_PIPE_STATE_OPENED;
+	p->w_state = LTTNG_PIPE_STATE_OPENED;
+	p->flags = flags;
+
+	return p;
+
+error:
+	lttng_pipe_destroy(p);
+	return NULL;
+}
+
+/*
+ * Close both read and write side of a lttng pipe.
+ *
+ * Return 0 on success else a negative value.
+ */
+int lttng_pipe_close(struct lttng_pipe *pipe)
+{
+	int ret, ret_val = 0;
+
+	assert(pipe);
+
+	/* Handle read side first. */
+	lock_read_side(pipe);
+	if (LTTNG_PIPE_IS_READ_OPEN(pipe)) {
+		ret = close(pipe->fd[0]);
+		if (ret < 0) {
+			PERROR("close lttng read pipe");
+			ret_val = ret;
+		}
+		pipe->r_state = LTTNG_PIPE_STATE_CLOSED;
+	}
+	unlock_read_side(pipe);
+
+	/* Handle write side. */
+	lock_write_side(pipe);
+	if (LTTNG_PIPE_IS_WRITE_OPEN(pipe)) {
+		ret = close(pipe->fd[0]);
+		if (ret < 0) {
+			PERROR("close lttng write pipe");
+			ret_val = ret;
+		}
+		pipe->w_state = LTTNG_PIPE_STATE_CLOSED;
+	}
+	unlock_write_side(pipe);
+
+	return ret_val;
+}
+
+/*
+ * Close and destroy a lttng pipe object. Finally, pipe is freed.
+ */
+void lttng_pipe_destroy(struct lttng_pipe *pipe)
+{
+	if (!pipe) {
+		return;
+	}
+
+	/* If pipe is already closed or not opened, this returns gracefully. */
+	(void) lttng_pipe_close(pipe);
+
+	(void) pthread_mutex_destroy(&pipe->read_mutex);
+	(void) pthread_mutex_destroy(&pipe->write_mutex);
+	free(pipe);
+}
+
+/*
+ * Read on a lttng pipe and put the data in buf of at least size count.
+ *
+ * Return 0 on success or else a negative errno message from read(2).
+ */
+ssize_t lttng_pipe_read(struct lttng_pipe *pipe, void *buf, size_t count)
+{
+	ssize_t ret, read_len, read_left, index;
+
+	assert(pipe);
+	assert(buf);
+
+	lock_read_side(pipe);
+
+	if (!LTTNG_PIPE_IS_READ_OPEN(pipe)) {
+		ret = -EBADF;
+		goto error;
+	}
+
+	read_left = count;
+	index = 0;
+	do {
+		read_len = read(pipe->fd[0], buf + index, read_left);
+		if (read_len < 0) {
+			switch (errno) {
+			case EINTR:
+				/* Read again. */
+				continue;
+			default:
+				PERROR("lttng pipe read");
+				ret = -errno;
+				goto error;
+			}
+		}
+		read_left -= read_len;
+		index += read_len;
+	} while (read_left > 0);
+
+	/* Everything went fine. */
+	ret = 0;
+
+error:
+	unlock_read_side(pipe);
+	return ret;
+}
+
+/*
+ * Write on a lttng pipe using the data in buf and size of count.
+ *
+ * Return 0 on success or else a negative errno message from write(2).
+ */
+ssize_t lttng_pipe_write(struct lttng_pipe *pipe, const void *buf,
+		size_t count)
+{
+	ssize_t ret, write_len, write_left, index;
+
+	assert(pipe);
+	assert(buf);
+
+	lock_write_side(pipe);
+
+	if (!LTTNG_PIPE_IS_WRITE_OPEN(pipe)) {
+		ret = -EBADF;
+		goto error;
+	}
+
+	write_left = count;
+	index = 0;
+	do {
+		write_len = write(pipe->fd[1], buf + index, write_left);
+		if (write_len < 0) {
+			switch (errno) {
+			case EINTR:
+				/* Write again. */
+				continue;
+			default:
+				PERROR("lttng pipe write");
+				ret = -errno;
+				goto error;
+			}
+		}
+		write_left -= write_len;
+		index += write_len;
+	} while (write_left > 0);
+
+	/* Everything went fine. */
+	ret = 0;
+
+error:
+	unlock_write_side(pipe);
+	return ret;
+}
diff --git a/src/common/pipe.h b/src/common/pipe.h
new file mode 100644
index 0000000..fdff4cb
--- /dev/null
+++ b/src/common/pipe.h
@@ -0,0 +1,62 @@
+/*
+ * Copyright (C) 2013 - David Goulet <dgoulet at efficios.com>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License, version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program; if not, write to the Free Software Foundation, Inc., 51
+ * Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifndef LTTNG_PIPE_H
+#define LTTNG_PIPE_H
+
+#include <pthread.h>
+
+#define LTTNG_PIPE_IS_READ_OPEN(p) \
+	(p->r_state == LTTNG_PIPE_STATE_OPENED ? 1 : 0)
+#define LTTNG_PIPE_IS_WRITE_OPEN(p) \
+	(p->w_state == LTTNG_PIPE_STATE_OPENED ? 1 : 0)
+
+enum lttng_pipe_state {
+	LTTNG_PIPE_STATE_OPENED = 1,
+	LTTNG_PIPE_STATE_CLOSED = 2,
+};
+
+struct lttng_pipe {
+	/* Read: 0, Write: 1. */
+	int fd[2];
+	/*
+	 * Flags of the pipe once opened. pipe(2) specifies either O_NONBLOCK or
+	 * O_CLOEXEC can be used. Flags are set using fcntl(2) call.
+	 */
+	int flags;
+
+	/*
+	 * These states are protected by the operation mutex below.
+	 */
+	enum lttng_pipe_state r_state;
+	enum lttng_pipe_state w_state;
+
+	/* Held for each read(2) operation. */
+	pthread_mutex_t read_mutex;
+	/* Held for each write(2) operation. */
+	pthread_mutex_t write_mutex;
+};
+
+struct lttng_pipe *lttng_pipe_open(int flags);
+int lttng_pipe_close(struct lttng_pipe *pipe);
+void lttng_pipe_destroy(struct lttng_pipe *pipe);
+
+ssize_t lttng_pipe_read(struct lttng_pipe *pipe, void *buf, size_t count);
+ssize_t lttng_pipe_write(struct lttng_pipe *pipe, const void *buf,
+		size_t count);
+
+#endif /* LTTNG_PIPE_H */
-- 
1.7.10.4




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