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log: Support multiple magic.
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Some OVSDB tools will want to open files that might be standalone or
clustered databases, and so it's better if ovsdb_log_open() can accept more
than one valid "magic".  This commit makes that possible.

Signed-off-by: Ben Pfaff <blp@ovn.org>
Acked-by: Justin Pettit <jpettit@ovn.org>
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blp committed Dec 25, 2017
1 parent 71e4030 commit fed2775
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Showing 3 changed files with 117 additions and 47 deletions.
155 changes: 111 additions & 44 deletions ovsdb/log.c
View file
Expand Up @@ -88,13 +88,19 @@ static bool rename_open_files = false;
static bool rename_open_files = true;
#endif

static bool parse_header(char *header, const char **magicp,
unsigned long int *length,
uint8_t sha1[SHA1_DIGEST_SIZE]);
static bool is_magic_ok(const char *needle, const char *haystack);

/* 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'.
*
* 'magic' is a short text string put at the beginning of every record and used
* to distinguish one kind of log file from another. For a conventional OVSDB
* log file, use the OVSDB_MAGIC macro.
* log file, use the OVSDB_MAGIC macro. To accept more than one magic string,
* separate them with "|", e.g. "MAGIC 1|MAGIC 2".
*
* 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
Expand All @@ -107,12 +113,16 @@ ovsdb_log_open(const char *name, const char *magic,
{
struct lockfile *lockfile;
struct ovsdb_error *error;
struct ovsdb_log *file;
struct stat s;
FILE *stream;
int flags;
int fd;

/* If we can create a new file, we need to know what kind of magic to
* use, so there must be only one kind. */
if (open_mode == OVSDB_LOG_CREATE_EXCL || open_mode == OVSDB_LOG_CREATE) {
ovs_assert(!strchr(magic, '|'));
}
*filep = NULL;

ovs_assert(locking == -1 || locking == false || locking == true);
Expand Down Expand Up @@ -181,58 +191,93 @@ ovsdb_log_open(const char *name, const char *magic,
goto error_unlock;
}

if (!fstat(fd, &s)) {
if (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);
} else if (s.st_size >= strlen(magic) && S_ISREG(s.st_mode)) {
/* Try to read the magic from the first log record. If it's not
* the magic we expect, this is the wrong kind of file, so reject
* it immediately. */
size_t magic_len = strlen(magic);
char *buf = xzalloc(magic_len + 1);
bool err = (read(fd, buf, magic_len) == magic_len
&& strcmp(buf, magic));
free(buf);
if (err) {
error = ovsdb_error(NULL, "%s: bad magic (unexpected "
"kind of file)", name);
goto error_close;
}
if (lseek(fd, 0, SEEK_SET)) {
error = ovsdb_io_error(errno, "%s: seek failed", name);
goto error_close;
}
}
}

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;
close(fd);
goto error_unlock;
}

/* Read the magic from the first log record. */
char header[128];
const char *actual_magic;
if (!fgets(header, sizeof header, stream)) {
if (ferror(stream)) {
error = ovsdb_io_error(errno, "%s: read error", name);
goto error_fclose;
}

/* We need to be able to report what kind of file this is but we can't
* if it's empty and we accept more than one. */
if (strchr(magic, '|')) {
error = ovsdb_error(NULL, "%s: cannot identify file type", name);
goto error_fclose;
}
actual_magic = magic;

/* It's an empty file and therefore probably a new file, so fsync()
* its parent directory to ensure that its directory entry is
* committed to disk. */
fsync_parent_dir(name);
} else {
unsigned long int length;
uint8_t sha1[SHA1_DIGEST_SIZE];
if (!parse_header(header, &actual_magic, &length, sha1)) {
error = ovsdb_error(NULL, "%s: unexpected file format", name);
goto error_fclose;
} else if (!is_magic_ok(actual_magic, magic)) {
error = ovsdb_error(NULL, "%s: cannot identify file type", name);
goto error_fclose;
}
}

if (fseek(stream, 0, SEEK_SET)) {
error = ovsdb_io_error(errno, "%s: seek failed", name);
goto error_fclose;
}

file = xmalloc(sizeof *file);
struct ovsdb_log *file = xmalloc(sizeof *file);
file->state = OVSDB_LOG_READ;
file->error = NULL;
file->name = xstrdup(name);
file->magic = xstrdup(magic);
file->magic = xstrdup(actual_magic);
file->lockfile = lockfile;
file->stream = stream;
file->prev_offset = 0;
file->offset = 0;
*filep = file;
return NULL;

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

/* Returns true if 'needle' is one of the |-delimited words in 'haystack'. */
static bool
is_magic_ok(const char *needle, const char *haystack)
{
/* 'needle' can't be multiple words. */
if (strchr(needle, '|')) {
return false;
}

size_t n = strlen(needle);
for (;;) {
if (!strncmp(needle, haystack, n) && strchr("|", haystack[n])) {
return true;
}
haystack = strchr(haystack, '|');
if (!haystack) {
return false;
}
haystack++;
}
}

void
ovsdb_log_close(struct ovsdb_log *file)
{
Expand All @@ -248,20 +293,41 @@ ovsdb_log_close(struct ovsdb_log *file)
}
}

const char *
ovsdb_log_get_magic(const struct ovsdb_log *log)
{
return log->magic;
}

/* Attempts to parse 'header' as a header line for an OVSDB log record (as
* described in ovsdb(5)). Stores a pointer to the magic string in '*magicp',
* the length in *length, and the parsed sha1 value in sha1[].
*
* Modifies 'header' and points '*magicp' inside it.
*
* Returns true if successful, false on failure. */
static bool
parse_header(const char *magic, char *header, unsigned long int *length,
uint8_t sha1[SHA1_DIGEST_SIZE])
parse_header(char *header, const char **magicp,
unsigned long int *length, uint8_t sha1[SHA1_DIGEST_SIZE])
{
char *p;
/* 'header' must consist of "OVSDB "... */
const char lead[] = "OVSDB ";
if (strncmp(lead, header, strlen(lead))) {
return false;
}

/* 'header' must consist of a magic string... */
size_t magic_len = strlen(magic);
if (strncmp(header, magic, magic_len) || header[magic_len] != ' ') {
/* ...followed by a magic string... */
char *magic = header + strlen(lead);
size_t magic_len = strcspn(magic, " ");
if (magic[magic_len] != ' ') {
return false;
}
magic[magic_len] = '\0';
*magicp = magic;

/* ...followed by a length in bytes... */
*length = strtoul(header + magic_len + 1, &p, 10);
char *p;
*length = strtoul(magic + magic_len + 1, &p, 10);
if (!*length || *length == ULONG_MAX || *p != ' ') {
return false;
}
Expand Down Expand Up @@ -343,7 +409,6 @@ 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];
Expand All @@ -357,16 +422,18 @@ ovsdb_log_read(struct ovsdb_log *file, struct json **jsonp)
error = ovsdb_io_error(errno, "%s: read failed", file->name);
goto error;
}
off_t data_offset = file->offset + strlen(header);

if (!parse_header(file->magic, header, &data_length, expected_sha1)) {
const char *magic;
if (!parse_header(header, &magic, &data_length, expected_sha1)
|| strcmp(magic, file->magic)) {
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;
Expand Down Expand Up @@ -447,7 +514,7 @@ ovsdb_log_compose_record(const struct json *json,
/* Compose header. */
uint8_t sha1[SHA1_DIGEST_SIZE];
sha1_bytes(data->string, data->length, sha1);
ds_put_format(header, "%s %"PRIuSIZE" "SHA1_FMT"\n",
ds_put_format(header, "OVSDB %s %"PRIuSIZE" "SHA1_FMT"\n",
magic, data->length, SHA1_ARGS(sha1));
}

Expand Down
7 changes: 5 additions & 2 deletions ovsdb/log.h
View file
@@ -1,4 +1,4 @@
/* Copyright (c) 2009, 2010, 2011 Nicira, Inc.
/* Copyright (c) 2009, 2010, 2011, 2017 Nicira, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
Expand Down Expand Up @@ -31,14 +31,17 @@ enum ovsdb_log_open_mode {
OVSDB_LOG_CREATE /* Create or open file, read/write. */
};

#define OVSDB_MAGIC "OVSDB JSON"
/* 'magic' for use with ovsdb_log_open() for OVSDB databases (see ovsdb(5)). */
#define OVSDB_MAGIC "JSON"

struct ovsdb_error *ovsdb_log_open(const char *name, const char *magic,
enum ovsdb_log_open_mode,
int locking, struct ovsdb_log **)
OVS_WARN_UNUSED_RESULT;
void ovsdb_log_close(struct ovsdb_log *);

const char *ovsdb_log_get_magic(const struct ovsdb_log *);

struct ovsdb_error *ovsdb_log_read(struct ovsdb_log *, struct json **)
OVS_WARN_UNUSED_RESULT;
void ovsdb_log_unread(struct ovsdb_log *);
Expand Down
2 changes: 1 addition & 1 deletion tests/ovsdb-log.at
View file
Expand Up @@ -174,7 +174,7 @@ file: read: end of log
]], [ignore])
AT_CHECK(
[test-ovsdb log-io file read-only], [1], [],
[test-ovsdb: ovsdb error: file: bad magic (unexpected kind of file)
[test-ovsdb: ovsdb error: file: cannot identify file type
])
AT_CHECK([test -f .file.~lock~])
AT_CLEANUP
Expand Down

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