[lttng-dev] [PATCH lttng-tools v2] Add wrappers for pipe
David Goulet
dgoulet at efficios.com
Mon May 13 15:43:06 EDT 2013
Mathieu Desnoyers:
> * David Goulet (dgoulet at efficios.com) 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_close, write_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 | 315 ++++++++++++++++++++++++++++++++++++++++++++++++
>> src/common/pipe.h | 76 ++++++++++++
>> 3 files changed, 393 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..9242a09
>> --- /dev/null
>> +++ b/src/common/pipe.c
>> @@ -0,0 +1,315 @@
>> +/*
>> + * 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 read side of a lttng pipe.
>> + *
>> + * Return 0 on success else a negative value.
>> + */
>> +int lttng_pipe_read_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)) {
>> + do {
>> + ret = close(pipe->fd[0]);
>> + } while (ret < 0 && errno == EINTR);
>> + if (ret < 0) {
>> + PERROR("close lttng read pipe");
>> + ret_val = -errno;
>> + }
>> + pipe->r_state = LTTNG_PIPE_STATE_CLOSED;
>> + }
>> + unlock_read_side(pipe);
>> +
>> + return ret_val;
>> +}
>> +
>> +/*
>> + * Close write side of a lttng pipe.
>> + *
>> + * Return 0 on success else a negative value.
>> + */
>> +int lttng_pipe_write_close(struct lttng_pipe *pipe)
>> +{
>> + int ret, ret_val = 0;
>> +
>> + assert(pipe);
>> +
>> + lock_write_side(pipe);
>> + if (lttng_pipe_is_write_open(pipe)) {
>> + do {
>> + ret = close(pipe->fd[1]);
>> + } while (ret < 0 && errno == EINTR);
>> + if (ret < 0) {
>> + PERROR("close lttng write pipe");
>> + ret_val = -errno;
>> + }
>> + pipe->w_state = LTTNG_PIPE_STATE_CLOSED;
>> + }
>> + unlock_write_side(pipe);
>> +
>> + return ret_val;
>> +}
>> +
>> +/*
>> + * 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);
>> +
>> + ret = lttng_pipe_read_close(pipe);
>> + if (ret < 0) {
>> + ret_val = ret;
>> + }
>> +
>> + ret = lttng_pipe_write_close(pipe);
>> + if (ret < 0) {
>> + ret_val = ret;
>> + }
>> +
>> + return ret_val;
>> +}
>> +
>> +/*
>> + * Close and destroy a lttng pipe object. Finally, pipe is freed.
>> + */
>> +void lttng_pipe_destroy(struct lttng_pipe *pipe)
>> +{
>> + int ret;
>> +
>> + if (!pipe) {
>> + return;
>> + }
>> +
>> + /* Wrong code flow. Destroy should *never* be called with mutex locked. */
>> + ret = pthread_mutex_trylock(&pipe->read_mutex);
>> + assert(!ret);
>> + ret = pthread_mutex_trylock(&pipe->write_mutex);
>> + assert(!ret);
>
What should be done then ?
David
> the issue here is that you trylock, then succeed, and then take the
> locks again within close, thus deadlocking.
>
> The rest looks good, thanks!
>
> Mathieu
>
>> +
>> + /* 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) {
>> + ret = -errno;
>> + if (errno == EINTR) {
>> + /* Read again. */
>> + continue;
>> + } else if (errno == EAGAIN || errno == EWOULDBLOCK) {
>> + /*
>> + * Return the number of bytes read up to this point if any.
>> + */
>> + if (index) {
>> + ret = index;
>> + }
>> + goto error;
>> + } else {
>> + PERROR("lttng pipe read");
>> + goto error;
>> + }
>> + }
>> + read_left -= read_len;
>> + index += read_len;
>> + } while (read_left > 0);
>> +
>> + /* Everything went fine. */
>> + ret = index;
>> +
>> +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) {
>> + ret = -errno;
>> + if (errno == EINTR) {
>> + /* Read again. */
>> + continue;
>> + } else if (errno == EAGAIN || errno == EWOULDBLOCK) {
>> + /*
>> + * Return the number of bytes read up to this point if any.
>> + */
>> + if (index) {
>> + ret = index;
>> + }
>> + goto error;
>> + } else {
>> + PERROR("lttng pipe write");
>> + goto error;
>> + }
>> + }
>> + write_left -= write_len;
>> + index += write_len;
>> + } while (write_left > 0);
>> +
>> + /* Everything went fine. */
>> + ret = index;
>> +
>> +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..acd05d8
>> --- /dev/null
>> +++ b/src/common/pipe.h
>> @@ -0,0 +1,76 @@
>> +/*
>> + * 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>
>> +
>> +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;
>> +};
>> +
>> +/*
>> + * Return 1 if read side is open else 0.
>> + */
>> +static inline int lttng_pipe_is_read_open(struct lttng_pipe *pipe)
>> +{
>> + return pipe->r_state == LTTNG_PIPE_STATE_OPENED ? 1 : 0;
>> +}
>> +
>> +/*
>> + * Return 1 if write side is open else 0.
>> + */
>> +static inline int lttng_pipe_is_write_open(struct lttng_pipe *pipe)
>> +{
>> + return pipe->w_state == LTTNG_PIPE_STATE_OPENED ? 1 : 0;
>> +}
>> +
>> +struct lttng_pipe *lttng_pipe_open(int flags);
>> +int lttng_pipe_write_close(struct lttng_pipe *pipe);
>> +int lttng_pipe_read_close(struct lttng_pipe *pipe);
>> +/* Close both side of pipe. */
>> +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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>
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