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shared: add ring buffer

New "struct ring" object that implements a basic ring buffer for arbitrary
byte-streams. A new basic runtime test is also added.

This will be needed for our pty helpers for systemd-console and friends.
keep-around/964a6d9fb555cc86528eb1cc1f6d044f85584842
David Herrmann 9 years ago
parent
commit
e0dd92729e
  1. 1
      .gitignore
  2. 9
      Makefile.am
  3. 208
      src/shared/ring.c
  4. 59
      src/shared/ring.h
  5. 135
      src/test/test-ring.c

1
.gitignore

@ -180,6 +180,7 @@
/test-path-util
/test-prioq
/test-replace-var
/test-ring
/test-rtnl
/test-sched-prio
/test-sleep

9
Makefile.am

@ -801,6 +801,8 @@ libsystemd_shared_la_SOURCES = \
src/shared/clean-ipc.c \
src/shared/login-shared.c \
src/shared/login-shared.h \
src/shared/ring.c \
src/shared/ring.h \
src/shared/async.c \
src/shared/async.h
@ -1198,6 +1200,7 @@ tests += \
test-utf8 \
test-ellipsize \
test-util \
test-ring \
test-tmpfiles \
test-namespace \
test-date \
@ -1325,6 +1328,12 @@ test_util_SOURCES = \
test_util_LDADD = \
libsystemd-core.la
test_ring_SOURCES = \
src/test/test-ring.c
test_ring_LDADD = \
libsystemd-core.la
test_tmpfiles_SOURCES = \
src/test/test-tmpfiles.c

208
src/shared/ring.c

@ -0,0 +1,208 @@
/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
/***
This file is part of systemd.
Copyright 2014 David Herrmann <dh.herrmann@gmail.com>
systemd is free software; you can redistribute it and/or modify it
under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or
(at your option) any later version.
systemd 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
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with systemd; If not, see <http://www.gnu.org/licenses/>.
***/
#include <errno.h>
#include <inttypes.h>
#include <stdlib.h>
#include <string.h>
#include <sys/uio.h>
#include "macro.h"
#include "ring.h"
#define RING_MASK(_r, _v) ((_v) & ((_r)->size - 1))
void ring_flush(struct ring *r) {
assert(r);
r->start = 0;
r->used = 0;
}
void ring_clear(struct ring *r) {
free(r->buf);
zero(*r);
}
/*
* Get data pointers for current ring-buffer data. @vec must be an array of 2
* iovec objects. They are filled according to the data available in the
* ring-buffer. 0, 1 or 2 is returned according to the number of iovec objects
* that were filled (0 meaning buffer is empty).
*
* Hint: "struct iovec" is defined in <sys/uio.h> and looks like this:
* struct iovec {
* void *iov_base;
* size_t iov_len;
* };
*/
size_t ring_peek(struct ring *r, struct iovec *vec) {
assert(r);
if (r->used == 0) {
return 0;
} else if (r->start + r->used <= r->size) {
if (vec) {
vec[0].iov_base = &r->buf[r->start];
vec[0].iov_len = r->used;
}
return 1;
} else {
if (vec) {
vec[0].iov_base = &r->buf[r->start];
vec[0].iov_len = r->size - r->start;
vec[1].iov_base = r->buf;
vec[1].iov_len = r->used - (r->size - r->start);
}
return 2;
}
}
/*
* Copy data from the ring buffer into the linear external buffer @buf. Copy
* at most @size bytes. If the ring buffer size is smaller, copy less bytes and
* return the number of bytes copied.
*/
size_t ring_copy(struct ring *r, void *buf, size_t size) {
size_t l;
assert(r);
assert(buf);
if (size > r->used)
size = r->used;
if (size > 0) {
l = r->size - r->start;
if (size <= l) {
memcpy(buf, &r->buf[r->start], size);
} else {
memcpy(buf, &r->buf[r->start], l);
memcpy((uint8_t*)buf + l, r->buf, size - l);
}
}
return size;
}
/*
* Resize ring-buffer to size @nsize. @nsize must be a power-of-2, otherwise
* ring operations will behave incorrectly.
*/
static int ring_resize(struct ring *r, size_t nsize) {
uint8_t *buf;
size_t l;
assert(r);
assert(nsize > 0);
buf = malloc(nsize);
if (!buf)
return -ENOMEM;
if (r->used > 0) {
l = r->size - r->start;
if (r->used <= l) {
memcpy(buf, &r->buf[r->start], r->used);
} else {
memcpy(buf, &r->buf[r->start], l);
memcpy(&buf[l], r->buf, r->used - l);
}
}
free(r->buf);
r->buf = buf;
r->size = nsize;
r->start = 0;
return 0;
}
/*
* Resize ring-buffer to provide enough room for @add bytes of new data. This
* resizes the buffer if it is too small. It returns -ENOMEM on OOM and 0 on
* success.
*/
static int ring_grow(struct ring *r, size_t add) {
size_t need;
assert(r);
if (r->size - r->used >= add)
return 0;
need = r->used + add;
if (need <= r->used)
return -ENOMEM;
else if (need < 4096)
need = 4096;
need = ALIGN_POWER2(need);
if (need == 0)
return -ENOMEM;
return ring_resize(r, need);
}
/*
* Push @len bytes from @u8 into the ring buffer. The buffer is resized if it
* is too small. -ENOMEM is returned on OOM, 0 on success.
*/
int ring_push(struct ring *r, const void *u8, size_t size) {
int err;
size_t pos, l;
assert(r);
assert(u8);
if (size == 0)
return 0;
err = ring_grow(r, size);
if (err < 0)
return err;
pos = RING_MASK(r, r->start + r->used);
l = r->size - pos;
if (l >= size) {
memcpy(&r->buf[pos], u8, size);
} else {
memcpy(&r->buf[pos], u8, l);
memcpy(r->buf, (const uint8_t*)u8 + l, size - l);
}
r->used += size;
return 0;
}
/*
* Remove @len bytes from the start of the ring-buffer. Note that we protect
* against overflows so removing more bytes than available is safe.
*/
void ring_pull(struct ring *r, size_t size) {
assert(r);
if (size > r->used)
size = r->used;
r->start = RING_MASK(r, r->start + size);
r->used -= size;
}

59
src/shared/ring.h

@ -0,0 +1,59 @@
/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
#pragma once
/***
This file is part of systemd.
Copyright 2014 David Herrmann <dh.herrmann@gmail.com>
systemd is free software; you can redistribute it and/or modify it
under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or
(at your option) any later version.
systemd 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
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with systemd; If not, see <http://www.gnu.org/licenses/>.
***/
#include <errno.h>
#include <inttypes.h>
#include <stdlib.h>
#include <string.h>
#include <sys/uio.h>
struct ring {
uint8_t *buf; /* buffer or NULL */
size_t size; /* actual size of @buf */
size_t start; /* start position of ring */
size_t used; /* number of actually used bytes */
};
/* flush buffer so it is empty again */
void ring_flush(struct ring *r);
/* flush buffer, free allocated data and reset to initial state */
void ring_clear(struct ring *r);
/* get pointers to buffer data and their length */
size_t ring_peek(struct ring *r, struct iovec *vec);
/* copy data into external linear buffer */
size_t ring_copy(struct ring *r, void *buf, size_t size);
/* push data to the end of the buffer */
int ring_push(struct ring *r, const void *u8, size_t size);
/* pull data from the front of the buffer */
void ring_pull(struct ring *r, size_t size);
/* return size of occupied buffer in bytes */
static inline size_t ring_get_size(struct ring *r)
{
return r->used;
}

135
src/test/test-ring.c

@ -0,0 +1,135 @@
/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
/***
This file is part of systemd.
Copyright 2014 David Herrmann <dh.herrmann@gmail.com>
systemd is free software; you can redistribute it and/or modify it
under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or
(at your option) any later version.
systemd 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
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with systemd; If not, see <http://www.gnu.org/licenses/>.
***/
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <locale.h>
#include <errno.h>
#include "def.h"
#include "ring.h"
#include "util.h"
static void test_ring(void) {
static const char buf[8192];
struct ring r;
size_t l;
struct iovec vec[2];
int s;
memset(&r, 0, sizeof(r));
l = ring_peek(&r, vec);
assert_se(l == 0);
s = ring_push(&r, buf, 2048);
assert_se(!s);
assert_se(ring_get_size(&r) == 2048);
l = ring_peek(&r, vec);
assert_se(l == 1);
assert_se(vec[0].iov_len == 2048);
assert_se(!memcmp(vec[0].iov_base, buf, vec[0].iov_len));
assert_se(ring_get_size(&r) == 2048);
ring_pull(&r, 2048);
assert_se(ring_get_size(&r) == 0);
l = ring_peek(&r, vec);
assert_se(l == 0);
assert_se(ring_get_size(&r) == 0);
s = ring_push(&r, buf, 2048);
assert_se(!s);
assert_se(ring_get_size(&r) == 2048);
l = ring_peek(&r, vec);
assert_se(l == 1);
assert_se(vec[0].iov_len == 2048);
assert_se(!memcmp(vec[0].iov_base, buf, vec[0].iov_len));
assert_se(ring_get_size(&r) == 2048);
s = ring_push(&r, buf, 1);
assert_se(!s);
assert_se(ring_get_size(&r) == 2049);
l = ring_peek(&r, vec);
assert_se(l == 2);
assert_se(vec[0].iov_len == 2048);
assert_se(vec[1].iov_len == 1);
assert_se(!memcmp(vec[0].iov_base, buf, vec[0].iov_len));
assert_se(!memcmp(vec[1].iov_base, buf, vec[1].iov_len));
assert_se(ring_get_size(&r) == 2049);
ring_pull(&r, 2048);
assert_se(ring_get_size(&r) == 1);
l = ring_peek(&r, vec);
assert_se(l == 1);
assert_se(vec[0].iov_len == 1);
assert_se(!memcmp(vec[0].iov_base, buf, vec[0].iov_len));
assert_se(ring_get_size(&r) == 1);
ring_pull(&r, 1);
assert_se(ring_get_size(&r) == 0);
s = ring_push(&r, buf, 2048);
assert_se(!s);
assert_se(ring_get_size(&r) == 2048);
s = ring_push(&r, buf, 2049);
assert_se(!s);
assert_se(ring_get_size(&r) == 4097);
l = ring_peek(&r, vec);
assert_se(l == 1);
assert_se(vec[0].iov_len == 4097);
assert_se(!memcmp(vec[0].iov_base, buf, vec[0].iov_len));
assert_se(ring_get_size(&r) == 4097);
ring_pull(&r, 1);
assert_se(ring_get_size(&r) == 4096);
s = ring_push(&r, buf, 4096);
assert_se(!s);
assert_se(ring_get_size(&r) == 8192);
l = ring_peek(&r, vec);
assert_se(l == 2);
assert_se(vec[0].iov_len == 8191);
assert_se(vec[1].iov_len == 1);
assert_se(!memcmp(vec[0].iov_base, buf, vec[0].iov_len));
assert_se(!memcmp(vec[1].iov_base, buf, vec[1].iov_len));
assert_se(ring_get_size(&r) == 8192);
ring_clear(&r);
assert_se(ring_get_size(&r) == 0);
}
int main(int argc, char *argv[]) {
log_parse_environment();
log_open();
test_ring();
return 0;
}
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