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fsmonitor--daemon: define token-ids

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Teach fsmonitor--daemon to create token-ids and define the
overall token naming scheme.

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
This commit is contained in:
Jeff Hostetler
2020-12-17 12:58:14 -05:00
committed by Johannes Schindelin
parent d49f16408b
commit 6b4070e4ee
1 changed files with 107 additions and 1 deletions
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108
builtin/fsmonitor--daemon.c
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@@ -149,6 +149,112 @@ static int do_as_client__send_flush(void)
return 0;
}
/*
* Requests to and from a FSMonitor Protocol V2 provider use an opaque
* "token" as a virtual timestamp. Clients can request a summary of all
* created/deleted/modified files relative to a token. In the response,
* clients receive a new token for the next (relative) request.
*
*
* Token Format
* ============
*
* The contents of the token are private and provider-specific.
*
* For the built-in fsmonitor--daemon, we define a token as follows:
*
* "builtin" ":" <token_id> ":" <sequence_nr>
*
* The <token_id> is an arbitrary OPAQUE string, such as a GUID,
* UUID, or {timestamp,pid}. It is used to group all filesystem
* events that happened while the daemon was monitoring (and in-sync
* with the filesystem).
*
* Unlike FSMonitor Protocol V1, it is not defined as a timestamp
* and does not define less-than/greater-than relationships.
* (There are too many race conditions to rely on file system
* event timestamps.)
*
* The <sequence_nr> is a simple integer incremented for each event
* received. When a new <token_id> is created, the <sequence_nr> is
* reset to zero.
*
*
* About Token Ids
* ===============
*
* A new token_id is created:
*
* [1] each time the daemon is started.
*
* [2] any time that the daemon must re-sync with the filesystem
* (such as when the kernel drops or we miss events on a very
* active volume).
*
* [3] in response to a client "flush" command (for dropped event
* testing).
*
* [4] MAYBE We might want to change the token_id after very complex
* filesystem operations are performed, such as a directory move
* sequence that affects many files within. It might be simpler
* to just give up and fake a re-sync (and let the client do a
* full scan) than try to enumerate the effects of such a change.
*
* When a new token_id is created, the daemon is free to discard all
* cached filesystem events associated with any previous token_ids.
* Events associated with a non-current token_id will never be sent
* to a client. A token_id change implicitly means that the daemon
* has gap in its event history.
*
* Therefore, clients that present a token with a stale (non-current)
* token_id will always be given a trivial response.
*/
struct fsmonitor_token_data {
struct strbuf token_id;
struct fsmonitor_batch *batch_head;
struct fsmonitor_batch *batch_tail;
uint64_t client_ref_count;
};
static struct fsmonitor_token_data *fsmonitor_new_token_data(void)
{
static int test_env_value = -1;
static uint64_t flush_count = 0;
struct fsmonitor_token_data *token;
token = (struct fsmonitor_token_data *)xcalloc(1, sizeof(*token));
strbuf_init(&token->token_id, 0);
token->batch_head = NULL;
token->batch_tail = NULL;
token->client_ref_count = 0;
if (test_env_value < 0)
test_env_value = git_env_bool("GIT_TEST_FSMONITOR_TOKEN", 0);
if (!test_env_value) {
struct timeval tv;
struct tm tm;
time_t secs;
gettimeofday(&tv, NULL);
secs = tv.tv_sec;
gmtime_r(&secs, &tm);
strbuf_addf(&token->token_id,
"%"PRIu64".%d.%4d%02d%02dT%02d%02d%02d.%06ldZ",
flush_count++,
getpid(),
tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday,
tm.tm_hour, tm.tm_min, tm.tm_sec,
(long)tv.tv_usec);
} else {
strbuf_addf(&token->token_id, "test_%08x", test_env_value++);
}
return token;
}
static ipc_server_application_cb handle_client;
static int handle_client(void *data, const char *command,
@@ -330,7 +436,7 @@ static int fsmonitor_run_daemon(void)
pthread_mutex_init(&state.main_lock, NULL);
state.error_code = 0;
state.current_token_data = NULL;
state.current_token_data = fsmonitor_new_token_data();
state.test_client_delay_ms = 0;
/* Prepare to (recursively) watch the <worktree-root> directory. */