[mirror_ovs.git] / ovsdb / log.c

/* Copyright (c) 2009, 2010, 2011, 2012, 2013 Nicira, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at:
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include <config.h>

#include "log.h"

#include <errno.h>
#include <fcntl.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <unistd.h>

#include "json.h"
#include "lockfile.h"
#include "ovsdb.h"
#include "ovsdb-error.h"
#include "sha1.h"
#include "socket-util.h"
#include "transaction.h"
#include "util.h"

enum ovsdb_log_mode {
    OVSDB_LOG_READ,
    OVSDB_LOG_WRITE
};

struct ovsdb_log {
    off_t prev_offset;
    off_t offset;
    char *name;
    struct lockfile *lockfile;
    FILE *stream;
    struct ovsdb_error *read_error;
    bool write_error;
    enum ovsdb_log_mode mode;
};

/* Attempts to open 'name' with the specified 'open_mode'.  On success, stores
 * the new log into '*filep' and returns NULL; otherwise returns NULL and
 * stores NULL into '*filep'.
 *
 * Whether the file will be locked using lockfile_lock() depends on 'locking':
 * use true to lock it, false not to lock it, or -1 to lock it only if
 * 'open_mode' is a mode that allows writing.
 */
struct ovsdb_error *
ovsdb_log_open(const char *name, enum ovsdb_log_open_mode open_mode,
               int locking, struct ovsdb_log **filep)
{
    struct lockfile *lockfile;
    struct ovsdb_error *error;
    struct ovsdb_log *file;
    struct stat s;
    FILE *stream;
    int flags;
    int fd;

    *filep = NULL;

    ovs_assert(locking == -1 || locking == false || locking == true);
    if (locking < 0) {
        locking = open_mode != OVSDB_LOG_READ_ONLY;
    }
    if (locking) {
        int retval = lockfile_lock(name, &lockfile);
        if (retval) {
            error = ovsdb_io_error(retval, "%s: failed to lock lockfile",
                                   name);
            goto error;
        }
    } else {
        lockfile = NULL;
    }

    if (open_mode == OVSDB_LOG_READ_ONLY) {
        flags = O_RDONLY;
    } else if (open_mode == OVSDB_LOG_READ_WRITE) {
        flags = O_RDWR;
    } else if (open_mode == OVSDB_LOG_CREATE) {
#ifndef _WIN32
        if (stat(name, &s) == -1 && errno == ENOENT
            && lstat(name, &s) == 0 && S_ISLNK(s.st_mode)) {
            /* 'name' is a dangling symlink.  We want to create the file that
             * the symlink points to, but POSIX says that open() with O_EXCL
             * must fail with EEXIST if the named file is a symlink.  So, we
             * have to leave off O_EXCL and accept the race. */
            flags = O_RDWR | O_CREAT;
        } else {
            flags = O_RDWR | O_CREAT | O_EXCL;
        }
#else
        flags = O_RDWR | O_CREAT | O_EXCL;
#endif
    } else {
        OVS_NOT_REACHED();
    }
#ifdef _WIN32
    flags = flags | O_BINARY;
#endif
    fd = open(name, flags, 0666);
    if (fd < 0) {
        const char *op = open_mode == OVSDB_LOG_CREATE ? "create" : "open";
        error = ovsdb_io_error(errno, "%s: %s failed", op, name);
        goto error_unlock;
    }

    if (!fstat(fd, &s) && s.st_size == 0) {
        /* It's (probably) a new file so fsync() its parent directory to ensure
         * that its directory entry is committed to disk. */
        fsync_parent_dir(name);
    }

    stream = fdopen(fd, open_mode == OVSDB_LOG_READ_ONLY ? "rb" : "w+b");
    if (!stream) {
        error = ovsdb_io_error(errno, "%s: fdopen failed", name);
        goto error_close;
    }

    file = xmalloc(sizeof *file);
    file->name = xstrdup(name);
    file->lockfile = lockfile;
    file->stream = stream;
    file->prev_offset = 0;
    file->offset = 0;
    file->read_error = NULL;
    file->write_error = false;
    file->mode = OVSDB_LOG_READ;
    *filep = file;
    return NULL;

error_close:
    close(fd);
error_unlock:
    lockfile_unlock(lockfile);
error:
    return error;
}

void
ovsdb_log_close(struct ovsdb_log *file)
{
    if (file) {
        free(file->name);
        fclose(file->stream);
        lockfile_unlock(file->lockfile);
        ovsdb_error_destroy(file->read_error);
        free(file);
    }
}

static const char magic[] = "OVSDB JSON ";

static bool
parse_header(char *header, unsigned long int *length,
             uint8_t sha1[SHA1_DIGEST_SIZE])
{
    char *p;

    /* 'header' must consist of a magic string... */
    if (strncmp(header, magic, strlen(magic))) {
        return false;
    }

    /* ...followed by a length in bytes... */
    *length = strtoul(header + strlen(magic), &p, 10);
    if (!*length || *length == ULONG_MAX || *p != ' ') {
        return false;
    }
    p++;

    /* ...followed by a SHA-1 hash... */
    if (!sha1_from_hex(sha1, p)) {
        return false;
    }
    p += SHA1_HEX_DIGEST_LEN;

    /* ...and ended by a new-line. */
    if (*p != '\n') {
        return false;
    }

    return true;
}

struct ovsdb_log_read_cbdata {
    char input[4096];
    struct ovsdb_log *file;
    int error;
    unsigned long length;
};

static struct ovsdb_error *
parse_body(struct ovsdb_log *file, off_t offset, unsigned long int length,
           uint8_t sha1[SHA1_DIGEST_SIZE], struct json **jsonp)
{
    struct json_parser *parser;
    struct sha1_ctx ctx;

    sha1_init(&ctx);
    parser = json_parser_create(JSPF_TRAILER);

    while (length > 0) {
        char input[BUFSIZ];
        int chunk;

        chunk = MIN(length, sizeof input);
        if (fread(input, 1, chunk, file->stream) != chunk) {
            json_parser_abort(parser);
            return ovsdb_io_error(ferror(file->stream) ? errno : EOF,
                                  "%s: error reading %lu bytes "
                                  "starting at offset %lld", file->name,
                                  length, (long long int) offset);
        }
        sha1_update(&ctx, input, chunk);
        json_parser_feed(parser, input, chunk);
        length -= chunk;
    }

    sha1_final(&ctx, sha1);
    *jsonp = json_parser_finish(parser);
    return NULL;
}

struct ovsdb_error *
ovsdb_log_read(struct ovsdb_log *file, struct json **jsonp)
{
    uint8_t expected_sha1[SHA1_DIGEST_SIZE];
    uint8_t actual_sha1[SHA1_DIGEST_SIZE];
    struct ovsdb_error *error;
    off_t data_offset;
    unsigned long data_length;
    struct json *json;
    char header[128];

    *jsonp = json = NULL;

    if (file->read_error) {
        return ovsdb_error_clone(file->read_error);
    } else if (file->mode == OVSDB_LOG_WRITE) {
        return OVSDB_BUG("reading file in write mode");
    }

    if (!fgets(header, sizeof header, file->stream)) {
        if (feof(file->stream)) {
            error = NULL;
        } else {
            error = ovsdb_io_error(errno, "%s: read failed", file->name);
        }
        goto error;
    }

    if (!parse_header(header, &data_length, expected_sha1)) {
        error = ovsdb_syntax_error(NULL, NULL, "%s: parse error at offset "
                                   "%lld in header line \"%.*s\"",
                                   file->name, (long long int) file->offset,
                                   (int) strcspn(header, "\n"), header);
        goto error;
    }

    data_offset = file->offset + strlen(header);
    error = parse_body(file, data_offset, data_length, actual_sha1, &json);
    if (error) {
        goto error;
    }

    if (memcmp(expected_sha1, actual_sha1, SHA1_DIGEST_SIZE)) {
        error = ovsdb_syntax_error(NULL, NULL, "%s: %lu bytes starting at "
                                   "offset %lld have SHA-1 hash "SHA1_FMT" "
                                   "but should have hash "SHA1_FMT,
                                   file->name, data_length,
                                   (long long int) data_offset,
                                   SHA1_ARGS(actual_sha1),
                                   SHA1_ARGS(expected_sha1));
        goto error;
    }

    if (json->type == JSON_STRING) {
        error = ovsdb_syntax_error(NULL, NULL, "%s: %lu bytes starting at "
                                   "offset %lld are not valid JSON (%s)",
                                   file->name, data_length,
                                   (long long int) data_offset,
                                   json->u.string);
        goto error;
    }

    file->prev_offset = file->offset;
    file->offset = data_offset + data_length;
    *jsonp = json;
    return NULL;

error:
    file->read_error = ovsdb_error_clone(error);
    json_destroy(json);
    return error;
}

/* Causes the log record read by the previous call to ovsdb_log_read() to be
 * effectively discarded.  The next call to ovsdb_log_write() will overwrite
 * that previously read record.
 *
 * Calling this function more than once has no additional effect.
 *
 * This function is useful when ovsdb_log_read() successfully reads a record
 * but that record does not make sense at a higher level (e.g. it specifies an
 * invalid transaction). */
void
ovsdb_log_unread(struct ovsdb_log *file)
{
    ovs_assert(file->mode == OVSDB_LOG_READ);
    file->offset = file->prev_offset;
}

struct ovsdb_error *
ovsdb_log_write(struct ovsdb_log *file, struct json *json)
{
    uint8_t sha1[SHA1_DIGEST_SIZE];
    struct ovsdb_error *error;
    char *json_string;
    char header[128];
    size_t length;

    json_string = NULL;

    if (file->mode == OVSDB_LOG_READ || file->write_error) {
        file->mode = OVSDB_LOG_WRITE;
        file->write_error = false;
        if (fseeko(file->stream, file->offset, SEEK_SET)) {
            error = ovsdb_io_error(errno, "%s: cannot seek to offset %lld",
                                   file->name, (long long int) file->offset);
            goto error;
        }
        if (ftruncate(fileno(file->stream), file->offset)) {
            error = ovsdb_io_error(errno, "%s: cannot truncate to length %lld",
                                   file->name, (long long int) file->offset);
            goto error;
        }
    }

    if (json->type != JSON_OBJECT && json->type != JSON_ARRAY) {
        error = OVSDB_BUG("bad JSON type");
        goto error;
    }

    /* Compose content.  Add a new-line (replacing the null terminator) to make
     * the file easier to read, even though it has no semantic value.  */
    json_string = json_to_string(json, 0);
    length = strlen(json_string) + 1;
    json_string[length - 1] = '\n';

    /* Compose header. */
    sha1_bytes(json_string, length, sha1);
    snprintf(header, sizeof header, "%s%"PRIuSIZE" "SHA1_FMT"\n",
             magic, length, SHA1_ARGS(sha1));

    /* Write. */
    if (fwrite(header, strlen(header), 1, file->stream) != 1
        || fwrite(json_string, length, 1, file->stream) != 1
        || fflush(file->stream))
    {
        error = ovsdb_io_error(errno, "%s: write failed", file->name);

        /* Remove any partially written data, ignoring errors since there is
         * nothing further we can do. */
        ignore(ftruncate(fileno(file->stream), file->offset));

        goto error;
    }

    file->offset += strlen(header) + length;
    free(json_string);
    return NULL;

error:
    file->write_error = true;
    free(json_string);
    return error;
}

struct ovsdb_error *
ovsdb_log_commit(struct ovsdb_log *file)
{
    if (fsync(fileno(file->stream))) {
        return ovsdb_io_error(errno, "%s: fsync failed", file->name);
    }
    return NULL;
}

/* Returns the current offset into the file backing 'log', in bytes.  This
 * reflects the number of bytes that have been read or written in the file.  If
 * the whole file has been read, this is the file size. */
off_t
ovsdb_log_get_offset(const struct ovsdb_log *log)
{
    return log->offset;
}
Commit	Line	Data
a7bf837f	1	/* Copyright (c) 2009, 2010, 2011, 2012, 2013 Nicira, Inc.
f85f8ebb BP	2	*
	3	* Licensed under the Apache License, Version 2.0 (the "License");
	4	* you may not use this file except in compliance with the License.
	5	* You may obtain a copy of the License at:
	6	*
	7	* http://www.apache.org/licenses/LICENSE-2.0
	8	*
	9	* Unless required by applicable law or agreed to in writing, software
	10	* distributed under the License is distributed on an "AS IS" BASIS,
	11	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	12	* See the License for the specific language governing permissions and
	13	* limitations under the License.
	14	*/
	15
	16	#include <config.h>
	17
41709ccc	18	#include "log.h"
f85f8ebb	19
f85f8ebb BP	20	#include <errno.h>
	21	#include <fcntl.h>
	22	#include <stdlib.h>
	23	#include <string.h>
3762274e	24	#include <sys/stat.h>
f85f8ebb BP	25	#include <unistd.h>
	26
	27	#include "json.h"
	28	#include "lockfile.h"
41709ccc	29	#include "ovsdb.h"
f85f8ebb BP	30	#include "ovsdb-error.h"
f85f8ebb BP	31	#include "sha1.h"
8e71cf88	32	#include "socket-util.h"
41709ccc	33	#include "transaction.h"
f85f8ebb	34	#include "util.h"
5136ce49	35
41709ccc BP	36	enum ovsdb_log_mode {
	37	OVSDB_LOG_READ,
	38	OVSDB_LOG_WRITE
f85f8ebb BP	39	};
f85f8ebb BP	40
41709ccc	41	struct ovsdb_log {
43675e26	42	off_t prev_offset;
f85f8ebb BP	43	off_t offset;
	44	char *name;
	45	struct lockfile *lockfile;
	46	FILE *stream;
	47	struct ovsdb_error *read_error;
a7bf837f	48	bool write_error;
41709ccc	49	enum ovsdb_log_mode mode;
f85f8ebb BP	50	};
f85f8ebb BP	51
7446f148 BP	52	/* Attempts to open 'name' with the specified 'open_mode'. On success, stores
	53	* the new log into '*filep' and returns NULL; otherwise returns NULL and
	54	* stores NULL into '*filep'.
	55	*
	56	* Whether the file will be locked using lockfile_lock() depends on 'locking':
	57	* use true to lock it, false not to lock it, or -1 to lock it only if
	58	* 'open_mode' is a mode that allows writing.
	59	*/
f85f8ebb	60	struct ovsdb_error *
7446f148 BP	61	ovsdb_log_open(const char *name, enum ovsdb_log_open_mode open_mode,
7446f148 BP	62	int locking, struct ovsdb_log **filep)
f85f8ebb BP	63	{
	64	struct lockfile *lockfile;
	65	struct ovsdb_error *error;
41709ccc	66	struct ovsdb_log *file;
f85f8ebb BP	67	struct stat s;
f85f8ebb BP	68	FILE *stream;
7446f148	69	int flags;
f85f8ebb BP	70	int fd;
	71
	72	*filep = NULL;
	73
cb22974d	74	ovs_assert(locking == -1 \|\| locking == false \|\| locking == true);
7446f148 BP	75	if (locking < 0) {
	76	locking = open_mode != OVSDB_LOG_READ_ONLY;
	77	}
	78	if (locking) {
4770e795	79	int retval = lockfile_lock(name, &lockfile);
f85f8ebb BP	80	if (retval) {
	81	error = ovsdb_io_error(retval, "%s: failed to lock lockfile",
	82	name);
	83	goto error;
	84	}
	85	} else {
	86	lockfile = NULL;
	87	}
	88
7446f148 BP	89	if (open_mode == OVSDB_LOG_READ_ONLY) {
	90	flags = O_RDONLY;
	91	} else if (open_mode == OVSDB_LOG_READ_WRITE) {
	92	flags = O_RDWR;
	93	} else if (open_mode == OVSDB_LOG_CREATE) {
7470e8e6	94	#ifndef _WIN32
01ca539f BP	95	if (stat(name, &s) == -1 && errno == ENOENT
	96	&& lstat(name, &s) == 0 && S_ISLNK(s.st_mode)) {
	97	/* 'name' is a dangling symlink. We want to create the file that
	98	* the symlink points to, but POSIX says that open() with O_EXCL
	99	* must fail with EEXIST if the named file is a symlink. So, we
	100	* have to leave off O_EXCL and accept the race. */
	101	flags = O_RDWR \| O_CREAT;
	102	} else {
	103	flags = O_RDWR \| O_CREAT \| O_EXCL;
	104	}
7470e8e6 GS	105	#else
	106	flags = O_RDWR \| O_CREAT \| O_EXCL;
	107	#endif
7446f148	108	} else {
428b2edd	109	OVS_NOT_REACHED();
7446f148	110	}
3e94784c GS	111	#ifdef _WIN32
	112	flags = flags \| O_BINARY;
	113	#endif
f85f8ebb BP	114	fd = open(name, flags, 0666);
f85f8ebb BP	115	if (fd < 0) {
7446f148	116	const char *op = open_mode == OVSDB_LOG_CREATE ? "create" : "open";
f85f8ebb BP	117	error = ovsdb_io_error(errno, "%s: %s failed", op, name);
	118	goto error_unlock;
	119	}
	120
	121	if (!fstat(fd, &s) && s.st_size == 0) {
	122	/* It's (probably) a new file so fsync() its parent directory to ensure
	123	* that its directory entry is committed to disk. */
8e71cf88	124	fsync_parent_dir(name);
f85f8ebb BP	125	}
f85f8ebb BP	126
7446f148	127	stream = fdopen(fd, open_mode == OVSDB_LOG_READ_ONLY ? "rb" : "w+b");
f85f8ebb BP	128	if (!stream) {
	129	error = ovsdb_io_error(errno, "%s: fdopen failed", name);
	130	goto error_close;
	131	}
	132
	133	file = xmalloc(sizeof *file);
	134	file->name = xstrdup(name);
	135	file->lockfile = lockfile;
	136	file->stream = stream;
43675e26	137	file->prev_offset = 0;
f85f8ebb BP	138	file->offset = 0;
f85f8ebb BP	139	file->read_error = NULL;
a7bf837f	140	file->write_error = false;
41709ccc	141	file->mode = OVSDB_LOG_READ;
f85f8ebb BP	142	*filep = file;
	143	return NULL;
	144
	145	error_close:
	146	close(fd);
	147	error_unlock:
	148	lockfile_unlock(lockfile);
	149	error:
	150	return error;
	151	}
	152
	153	void
41709ccc	154	ovsdb_log_close(struct ovsdb_log *file)
f85f8ebb BP	155	{
	156	if (file) {
	157	free(file->name);
	158	fclose(file->stream);
	159	lockfile_unlock(file->lockfile);
	160	ovsdb_error_destroy(file->read_error);
f85f8ebb BP	161	free(file);
	162	}
	163	}
	164
	165	static const char magic[] = "OVSDB JSON ";
	166
	167	static bool
	168	parse_header(char header, unsigned long int length,
	169	uint8_t sha1[SHA1_DIGEST_SIZE])
	170	{
	171	char *p;
	172
	173	/* 'header' must consist of a magic string... */
	174	if (strncmp(header, magic, strlen(magic))) {
	175	return false;
	176	}
	177
	178	/* ...followed by a length in bytes... */
	179	*length = strtoul(header + strlen(magic), &p, 10);
	180	if (!length \|\| length == ULONG_MAX \|\| *p != ' ') {
	181	return false;
	182	}
	183	p++;
	184
	185	/* ...followed by a SHA-1 hash... */
	186	if (!sha1_from_hex(sha1, p)) {
	187	return false;
	188	}
	189	p += SHA1_HEX_DIGEST_LEN;
	190
	191	/* ...and ended by a new-line. */
	192	if (*p != '\n') {
	193	return false;
	194	}
	195
	196	return true;
	197	}
	198
41709ccc	199	struct ovsdb_log_read_cbdata {
f85f8ebb	200	char input[4096];
41709ccc	201	struct ovsdb_log *file;
f85f8ebb BP	202	int error;
	203	unsigned long length;
	204	};
	205
	206	static struct ovsdb_error *
41709ccc	207	parse_body(struct ovsdb_log *file, off_t offset, unsigned long int length,
f85f8ebb BP	208	uint8_t sha1[SHA1_DIGEST_SIZE], struct json **jsonp)
f85f8ebb BP	209	{
f85f8ebb BP	210	struct json_parser *parser;
	211	struct sha1_ctx ctx;
	212
	213	sha1_init(&ctx);
	214	parser = json_parser_create(JSPF_TRAILER);
	215
f85f8ebb BP	216	while (length > 0) {
	217	char input[BUFSIZ];
	218	int chunk;
	219
	220	chunk = MIN(length, sizeof input);
	221	if (fread(input, 1, chunk, file->stream) != chunk) {
	222	json_parser_abort(parser);
	223	return ovsdb_io_error(ferror(file->stream) ? errno : EOF,
	224	"%s: error reading %lu bytes "
	225	"starting at offset %lld", file->name,
	226	length, (long long int) offset);
	227	}
	228	sha1_update(&ctx, input, chunk);
	229	json_parser_feed(parser, input, chunk);
	230	length -= chunk;
	231	}
	232
	233	sha1_final(&ctx, sha1);
	234	*jsonp = json_parser_finish(parser);
	235	return NULL;
	236	}
	237
	238	struct ovsdb_error *
41709ccc	239	ovsdb_log_read(struct ovsdb_log file, struct json *jsonp)
f85f8ebb BP	240	{
	241	uint8_t expected_sha1[SHA1_DIGEST_SIZE];
	242	uint8_t actual_sha1[SHA1_DIGEST_SIZE];
	243	struct ovsdb_error *error;
	244	off_t data_offset;
	245	unsigned long data_length;
	246	struct json *json;
	247	char header[128];
	248
	249	*jsonp = json = NULL;
	250
	251	if (file->read_error) {
	252	return ovsdb_error_clone(file->read_error);
41709ccc	253	} else if (file->mode == OVSDB_LOG_WRITE) {
f85f8ebb BP	254	return OVSDB_BUG("reading file in write mode");
	255	}
	256
	257	if (!fgets(header, sizeof header, file->stream)) {
	258	if (feof(file->stream)) {
	259	error = NULL;
	260	} else {
	261	error = ovsdb_io_error(errno, "%s: read failed", file->name);
	262	}
	263	goto error;
	264	}
	265
	266	if (!parse_header(header, &data_length, expected_sha1)) {
	267	error = ovsdb_syntax_error(NULL, NULL, "%s: parse error at offset "
	268	"%lld in header line \"%.*s\"",
	269	file->name, (long long int) file->offset,
	270	(int) strcspn(header, "\n"), header);
	271	goto error;
	272	}
	273
	274	data_offset = file->offset + strlen(header);
	275	error = parse_body(file, data_offset, data_length, actual_sha1, &json);
	276	if (error) {
	277	goto error;
	278	}
	279
	280	if (memcmp(expected_sha1, actual_sha1, SHA1_DIGEST_SIZE)) {
	281	error = ovsdb_syntax_error(NULL, NULL, "%s: %lu bytes starting at "
	282	"offset %lld have SHA-1 hash "SHA1_FMT" "
	283	"but should have hash "SHA1_FMT,
	284	file->name, data_length,
	285	(long long int) data_offset,
	286	SHA1_ARGS(actual_sha1),
	287	SHA1_ARGS(expected_sha1));
	288	goto error;
	289	}
	290
	291	if (json->type == JSON_STRING) {
	292	error = ovsdb_syntax_error(NULL, NULL, "%s: %lu bytes starting at "
	293	"offset %lld are not valid JSON (%s)",
	294	file->name, data_length,
	295	(long long int) data_offset,
	296	json->u.string);
	297	goto error;
	298	}
	299
43675e26	300	file->prev_offset = file->offset;
f85f8ebb BP	301	file->offset = data_offset + data_length;
f85f8ebb BP	302	*jsonp = json;
e3c17733	303	return NULL;
f85f8ebb BP	304
	305	error:
	306	file->read_error = ovsdb_error_clone(error);
	307	json_destroy(json);
	308	return error;
	309	}
	310
43675e26 BP	311	/* Causes the log record read by the previous call to ovsdb_log_read() to be
	312	* effectively discarded. The next call to ovsdb_log_write() will overwrite
	313	* that previously read record.
	314	*
	315	* Calling this function more than once has no additional effect.
	316	*
	317	* This function is useful when ovsdb_log_read() successfully reads a record
	318	* but that record does not make sense at a higher level (e.g. it specifies an
	319	* invalid transaction). */
	320	void
	321	ovsdb_log_unread(struct ovsdb_log *file)
	322	{
cb22974d	323	ovs_assert(file->mode == OVSDB_LOG_READ);
43675e26 BP	324	file->offset = file->prev_offset;
	325	}
	326
f85f8ebb	327	struct ovsdb_error *
41709ccc	328	ovsdb_log_write(struct ovsdb_log file, struct json json)
f85f8ebb BP	329	{
	330	uint8_t sha1[SHA1_DIGEST_SIZE];
	331	struct ovsdb_error *error;
	332	char *json_string;
	333	char header[128];
	334	size_t length;
	335
	336	json_string = NULL;
	337
a7bf837f	338	if (file->mode == OVSDB_LOG_READ \|\| file->write_error) {
41709ccc	339	file->mode = OVSDB_LOG_WRITE;
a7bf837f	340	file->write_error = false;
f85f8ebb BP	341	if (fseeko(file->stream, file->offset, SEEK_SET)) {
	342	error = ovsdb_io_error(errno, "%s: cannot seek to offset %lld",
	343	file->name, (long long int) file->offset);
	344	goto error;
	345	}
	346	if (ftruncate(fileno(file->stream), file->offset)) {
	347	error = ovsdb_io_error(errno, "%s: cannot truncate to length %lld",
	348	file->name, (long long int) file->offset);
	349	goto error;
	350	}
	351	}
	352
	353	if (json->type != JSON_OBJECT && json->type != JSON_ARRAY) {
	354	error = OVSDB_BUG("bad JSON type");
	355	goto error;
	356	}
	357
	358	/* Compose content. Add a new-line (replacing the null terminator) to make
	359	* the file easier to read, even though it has no semantic value. */
	360	json_string = json_to_string(json, 0);
	361	length = strlen(json_string) + 1;
	362	json_string[length - 1] = '\n';
	363
	364	/* Compose header. */
	365	sha1_bytes(json_string, length, sha1);
34582733	366	snprintf(header, sizeof header, "%s%"PRIuSIZE" "SHA1_FMT"\n",
f85f8ebb BP	367	magic, length, SHA1_ARGS(sha1));
	368
	369	/* Write. */
	370	if (fwrite(header, strlen(header), 1, file->stream) != 1
	371	\|\| fwrite(json_string, length, 1, file->stream) != 1
	372	\|\| fflush(file->stream))
	373	{
	374	error = ovsdb_io_error(errno, "%s: write failed", file->name);
	375
	376	/* Remove any partially written data, ignoring errors since there is
	377	* nothing further we can do. */
18b9283b	378	ignore(ftruncate(fileno(file->stream), file->offset));
f85f8ebb BP	379
	380	goto error;
	381	}
	382
	383	file->offset += strlen(header) + length;
	384	free(json_string);
e3c17733	385	return NULL;
f85f8ebb BP	386
f85f8ebb BP	387	error:
a7bf837f	388	file->write_error = true;
f85f8ebb BP	389	free(json_string);
	390	return error;
	391	}
	392
	393	struct ovsdb_error *
41709ccc	394	ovsdb_log_commit(struct ovsdb_log *file)
f85f8ebb BP	395	{
	396	if (fsync(fileno(file->stream))) {
	397	return ovsdb_io_error(errno, "%s: fsync failed", file->name);
	398	}
e3c17733	399	return NULL;
f85f8ebb	400	}
41709ccc	401
ada496b5 BP	402	/* Returns the current offset into the file backing 'log', in bytes. This
	403	* reflects the number of bytes that have been read or written in the file. If
	404	* the whole file has been read, this is the file size. */
	405	off_t
	406	ovsdb_log_get_offset(const struct ovsdb_log *log)
	407	{
	408	return log->offset;
	409	}