* David Goulet ([email protected]) wrote:
> 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 <[email protected]>
> ---
> 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 <[email protected]>
> + *
> + * 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)
we could split in pipe_close read vs write ?
> +{
> + 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;
> + }
> +
we could add interesting asserts here:
if any of read/write lock is currently locked, fail with an assert. It
is incorrect to have a concurrent thread using the pipe while we destroy
it.
> + /* 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).
I would prefer that we return similar return values to read(). We expect
"count - read_left" I guess.
> + */
> +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;
If we already have been able to read a some bytes in the previous
passes, shouldn't we return that number of bytes instead ?
> + 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).
Similar comments about ret values as read above.
> + */
> +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 <[email protected]>
> + *
> + * 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)
those two could be static inline. no need for macros.
Thanks,
Mathieu
> +
> +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
>
>
> _______________________________________________
> lttng-dev mailing list
> [email protected]
> http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
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