git/lib/trace2/tr2_dst.c

#include "git-compat-util.h"
#include "abspath.h"
#include "sigchain.h"
#include "strbuf.h"
#include "trace2/tr2_dst.h"
#include "trace2/tr2_sid.h"
#include "trace2/tr2_sysenv.h"

/*
 * How many attempts we will make at creating an automatically-named trace file.
 */
#define MAX_AUTO_ATTEMPTS 10

/*
 * Sentinel file used to detect when we should discard new traces to avoid
 * writing too many trace files to a directory.
 */
#define DISCARD_SENTINEL_NAME "git-trace2-discard"

/*
 * When set to zero, disables directory file count checks. Otherwise, controls
 * how many files we can write to a directory before entering discard mode.
 * This can be overridden via the TR2_SYSENV_MAX_FILES setting.
 */
static int tr2env_max_files = 0;

static int tr2_dst_want_warning(void)
{
	static int tr2env_dst_debug = -1;

	if (tr2env_dst_debug == -1) {
		const char *env_value = tr2_sysenv_get(TR2_SYSENV_DST_DEBUG);
		if (!env_value || !*env_value)
			tr2env_dst_debug = 0;
		else
			tr2env_dst_debug = atoi(env_value) > 0;
	}

	return tr2env_dst_debug;
}

void tr2_dst_trace_disable(struct tr2_dst *dst)
{
	if (dst->need_close)
		close(dst->fd);
	dst->fd = 0;
	dst->initialized = 1;
	dst->need_close = 0;
}

/*
 * Check to make sure we're not overloading the target directory with too many
 * files. First get the threshold (if present) from the config or envvar. If
 * it's zero or unset, disable this check. Next check for the presence of a
 * sentinel file, then check file count.
 *
 * Returns 0 if tracing should proceed as normal. Returns 1 if the sentinel file
 * already exists, which means tracing should be disabled. Returns -1 if there
 * are too many files but there was no sentinel file, which means we have
 * created and should write traces to the sentinel file.
 *
 * We expect that some trace processing system is gradually collecting files
 * from the target directory; after it removes the sentinel file we'll start
 * writing traces again.
 */
static int tr2_dst_too_many_files(struct tr2_dst *dst, const char *tgt_prefix)
{
	int file_count = 0, max_files = 0, ret = 0;
	const char *max_files_var;
	DIR *dirp;
	struct strbuf path = STRBUF_INIT, sentinel_path = STRBUF_INIT;
	struct stat statbuf;

	/* Get the config or envvar and decide if we should continue this check */
	max_files_var = tr2_sysenv_get(TR2_SYSENV_MAX_FILES);
	if (max_files_var && *max_files_var && ((max_files = atoi(max_files_var)) >= 0))
		tr2env_max_files = max_files;

	if (!tr2env_max_files) {
		ret = 0;
		goto cleanup;
	}

	strbuf_addstr(&path, tgt_prefix);
	if (!is_dir_sep(path.buf[path.len - 1])) {
		strbuf_addch(&path, '/');
	}

	/* check sentinel */
	strbuf_addbuf(&sentinel_path, &path);
	strbuf_addstr(&sentinel_path, DISCARD_SENTINEL_NAME);
	if (!stat(sentinel_path.buf, &statbuf)) {
		ret = 1;
		goto cleanup;
	}

	/* check file count */
	dirp = opendir(path.buf);
	while (file_count < tr2env_max_files && dirp && readdir(dirp))
		file_count++;
	if (dirp)
		closedir(dirp);

	if (file_count >= tr2env_max_files) {
		dst->too_many_files = 1;
		dst->fd = open(sentinel_path.buf, O_WRONLY | O_CREAT | O_EXCL, 0666);
		ret = -1;
		goto cleanup;
	}

cleanup:
	strbuf_release(&path);
	strbuf_release(&sentinel_path);
	return ret;
}

static int tr2_dst_try_auto_path(struct tr2_dst *dst, const char *tgt_prefix)
{
	int too_many_files;
	const char *last_slash, *sid = tr2_sid_get();
	struct strbuf path = STRBUF_INIT;
	size_t base_path_len;
	unsigned attempt_count;

	last_slash = strrchr(sid, '/');
	if (last_slash)
		sid = last_slash + 1;

	strbuf_addstr(&path, tgt_prefix);
	if (!is_dir_sep(path.buf[path.len - 1]))
		strbuf_addch(&path, '/');
	strbuf_addstr(&path, sid);
	base_path_len = path.len;

	too_many_files = tr2_dst_too_many_files(dst, tgt_prefix);
	if (!too_many_files) {
		for (attempt_count = 0; attempt_count < MAX_AUTO_ATTEMPTS; attempt_count++) {
			if (attempt_count > 0) {
				strbuf_setlen(&path, base_path_len);
				strbuf_addf(&path, ".%d", attempt_count);
			}

			dst->fd = open(path.buf, O_WRONLY | O_CREAT | O_EXCL, 0666);
			if (dst->fd != -1)
				break;
		}
	} else if (too_many_files == 1) {
		strbuf_release(&path);
		if (tr2_dst_want_warning())
			warning("trace2: not opening %s trace file due to too "
				"many files in target directory %s",
				tr2_sysenv_display_name(dst->sysenv_var),
				tgt_prefix);
		return 0;
	}

	if (dst->fd == -1) {
		if (tr2_dst_want_warning())
			warning("trace2: could not open '%.*s' for '%s' tracing: %s",
				(int) base_path_len, path.buf,
				tr2_sysenv_display_name(dst->sysenv_var),
				strerror(errno));

		tr2_dst_trace_disable(dst);
		strbuf_release(&path);
		return 0;
	}

	strbuf_release(&path);

	dst->need_close = 1;
	dst->initialized = 1;

	return dst->fd;
}

static int tr2_dst_try_path(struct tr2_dst *dst, const char *tgt_value)
{
	int fd = open(tgt_value, O_WRONLY | O_APPEND | O_CREAT, 0666);
	if (fd == -1) {
		if (tr2_dst_want_warning())
			warning("trace2: could not open '%s' for '%s' tracing: %s",
				tgt_value,
				tr2_sysenv_display_name(dst->sysenv_var),
				strerror(errno));

		tr2_dst_trace_disable(dst);
		return 0;
	}

	dst->fd = fd;
	dst->need_close = 1;
	dst->initialized = 1;

	return dst->fd;
}

#ifndef NO_UNIX_SOCKETS
#define PREFIX_AF_UNIX "af_unix:"
#define PREFIX_AF_UNIX_STREAM "af_unix:stream:"
#define PREFIX_AF_UNIX_DGRAM "af_unix:dgram:"

static int tr2_dst_try_uds_connect(const char *path, int sock_type, int *out_fd)
{
	int fd;
	struct sockaddr_un sa;

	fd = socket(AF_UNIX, sock_type, 0);
	if (fd == -1)
		return -1;

	sa.sun_family = AF_UNIX;
	strlcpy(sa.sun_path, path, sizeof(sa.sun_path));

	if (connect(fd, (struct sockaddr *)&sa, sizeof(sa)) == -1) {
		int saved_errno = errno;
		close(fd);
		errno = saved_errno;
		return -1;
	}

	*out_fd = fd;
	return 0;
}

#define TR2_DST_UDS_TRY_STREAM (1 << 0)
#define TR2_DST_UDS_TRY_DGRAM  (1 << 1)

static int tr2_dst_try_unix_domain_socket(struct tr2_dst *dst,
					  const char *tgt_value)
{
	unsigned int uds_try = 0;
	int fd;
	const char *path = NULL;

	/*
	 * Allow "af_unix:[<type>:]<absolute_path>"
	 *
	 * Trace2 always writes complete individual messages (without
	 * chunking), so we can talk to either DGRAM or STREAM type sockets.
	 *
	 * Allow the user to explicitly request the socket type.
	 *
	 * If they omit the socket type, try one and then the other.
	 */

	if (skip_prefix(tgt_value, PREFIX_AF_UNIX_STREAM, &path))
		uds_try |= TR2_DST_UDS_TRY_STREAM;

	else if (skip_prefix(tgt_value, PREFIX_AF_UNIX_DGRAM, &path))
		uds_try |= TR2_DST_UDS_TRY_DGRAM;

	else if (skip_prefix(tgt_value, PREFIX_AF_UNIX, &path))
		uds_try |= TR2_DST_UDS_TRY_STREAM | TR2_DST_UDS_TRY_DGRAM;

	if (!path || !*path) {
		if (tr2_dst_want_warning())
			warning("trace2: invalid AF_UNIX value '%s' for '%s' tracing",
				tgt_value,
				tr2_sysenv_display_name(dst->sysenv_var));

		tr2_dst_trace_disable(dst);
		return 0;
	}

	if (!is_absolute_path(path) ||
	    strlen(path) >= sizeof(((struct sockaddr_un *)0)->sun_path)) {
		if (tr2_dst_want_warning())
			warning("trace2: invalid AF_UNIX path '%s' for '%s' tracing",
				path, tr2_sysenv_display_name(dst->sysenv_var));

		tr2_dst_trace_disable(dst);
		return 0;
	}

	if (uds_try & TR2_DST_UDS_TRY_STREAM) {
		if (!tr2_dst_try_uds_connect(path, SOCK_STREAM, &fd))
			goto connected;
		if (errno != EPROTOTYPE)
			goto error;
	}
	if (uds_try & TR2_DST_UDS_TRY_DGRAM) {
		if (!tr2_dst_try_uds_connect(path, SOCK_DGRAM, &fd))
			goto connected;
	}

error:
	if (tr2_dst_want_warning())
		warning("trace2: could not connect to socket '%s' for '%s' tracing: %s",
			path, tr2_sysenv_display_name(dst->sysenv_var),
			strerror(errno));

	tr2_dst_trace_disable(dst);
	return 0;

connected:
	dst->fd = fd;
	dst->need_close = 1;
	dst->initialized = 1;

	return dst->fd;
}
#endif

static void tr2_dst_malformed_warning(struct tr2_dst *dst,
				      const char *tgt_value)
{
	warning("trace2: unknown value for '%s': '%s'",
		tr2_sysenv_display_name(dst->sysenv_var), tgt_value);
}

int tr2_dst_get_trace_fd(struct tr2_dst *dst)
{
	const char *tgt_value;

	/* don't open twice */
	if (dst->initialized)
		return dst->fd;

	dst->initialized = 1;

	tgt_value = tr2_sysenv_get(dst->sysenv_var);

	if (!tgt_value || !strcmp(tgt_value, "") || !strcmp(tgt_value, "0") ||
	    !strcasecmp(tgt_value, "false")) {
		dst->fd = 0;
		return dst->fd;
	}

	if (!strcmp(tgt_value, "1") || !strcasecmp(tgt_value, "true")) {
		dst->fd = STDERR_FILENO;
		return dst->fd;
	}

	if (strlen(tgt_value) == 1 && isdigit(*tgt_value)) {
		dst->fd = atoi(tgt_value);
		return dst->fd;
	}

	if (is_absolute_path(tgt_value)) {
		if (is_directory(tgt_value))
			return tr2_dst_try_auto_path(dst, tgt_value);
		else
			return tr2_dst_try_path(dst, tgt_value);
	}

#ifndef NO_UNIX_SOCKETS
	if (starts_with(tgt_value, PREFIX_AF_UNIX))
		return tr2_dst_try_unix_domain_socket(dst, tgt_value);
#endif

	/* Always warn about malformed values. */
	tr2_dst_malformed_warning(dst, tgt_value);
	tr2_dst_trace_disable(dst);
	return 0;
}

int tr2_dst_trace_want(struct tr2_dst *dst)
{
	return !!tr2_dst_get_trace_fd(dst);
}

void tr2_dst_write_line(struct tr2_dst *dst, struct strbuf *buf_line)
{
	int fd = tr2_dst_get_trace_fd(dst);
	ssize_t bytes;

	strbuf_complete_line(buf_line); /* ensure final NL on buffer */

	/*
	 * We do not use write_in_full() because we do not want
	 * a short-write to try again.  We are using O_APPEND mode
	 * files and the kernel handles the atomic seek+write. If
	 * another thread or git process is concurrently writing to
	 * this fd or file, our remainder-write may not be contiguous
	 * with our initial write of this message.  And that will
	 * confuse readers.  So just don't bother.
	 *
	 * It is assumed that TRACE2 messages are short enough that
	 * the system can write them in 1 attempt and we won't see
	 * a short-write.
	 *
	 * If we get an IO error, just close the trace dst.
	 */
	sigchain_push(SIGPIPE, SIG_IGN);
	bytes = write(fd, buf_line->buf, buf_line->len);
	sigchain_pop(SIGPIPE);
	if (bytes >= 0)
		return;

	tr2_dst_trace_disable(dst);
	if (tr2_dst_want_warning())
		warning("unable to write trace to '%s': %s",
			tr2_sysenv_display_name(dst->sysenv_var),
			strerror(errno));
}