On Thu, Mar 21 2019, Josh Steadmon wrote:
> When the value of a trace2 environment variable is an absolute path
> referring to an existing directory, write output to files (one per
> process) underneath the given directory. Files will be named according
> to the final component of the trace2 SID, followed by a counter to avoid
> potential collisions.
Is this "counter to avoid collisions" something you've seen the need to
have in practice, or could we just squash this on top:
diff --git a/trace2/tr2_dst.c b/trace2/tr2_dst.c
index c3d82ca6a4..06cbef5837 100644
--- a/trace2/tr2_dst.c
+++ b/trace2/tr2_dst.c
@@ -13,11 +13,6 @@
*/
#define TR2_ENVVAR_DST_DEBUG "GIT_TR2_DST_DEBUG"
-/*
- * How many attempts we will make at creating an automatically-named trace
file.
- */
-#define MAX_AUTO_ATTEMPTS 10
-
static int tr2_dst_want_warning(void)
{
static int tr2env_dst_debug = -1;
@@ -48,7 +43,6 @@ static int tr2_dst_try_auto_path(struct tr2_dst *dst,
const char *tgt_prefix)
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)
@@ -60,17 +54,7 @@ static int tr2_dst_try_auto_path(struct tr2_dst *dst,
const char *tgt_prefix)
strbuf_addstr(&path, sid);
base_path_len = path.len;
- 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);
- }
-
- fd = open(path.buf, O_WRONLY | O_CREAT | O_EXCL, 0666);
- if (fd != -1)
- break;
- }
-
+ fd = open(path.buf, O_WRONLY | O_CREAT | O_EXCL, 0666);
if (fd == -1) {
if (tr2_dst_want_warning())
warning("trace2: could not open '%.*s' for '%s'
tracing: %s",
The reason I'm raising this is that it seems like sweeping an existing
issue under the rug. We document that the "sid" is "unique", and it's just:
<nanotime / 1000 (i.e. *nix time in microseconds)>-<pid>
So that might be a lie, and in particular I can imagine that say if
every machine at Google is logging traces into some magic mounted FS
that there'll be collisions there.
But then let's *fix that*, because we're also e.g. going to have other
consumers of these traces using the sid's as primary keys in a logging
system.
I wonder if we should just make it a bit longer, human-readable, and
include a hash of the hostname:
perl -MTime::HiRes=gettimeofday -MSys::Hostname -MDigest::SHA=sha1_hex
-MPOSIX=strftime -wE '
my ($t, $m) = gettimeofday;
my $host_hex = substr sha1_hex(hostname()), 0, 8;
my $htime = strftime("%Y%m%d%H%M%S", localtime);
my $sid = sprintf("%s-%6d-%s-%s",
$htime,
$m,
$host_hex,
$$ & 0xFFFF,
);
say $sid;
'
Which gets you a SID like:
20190323213918-404788-c2f5b994-19027
I.e.:
<YYYYMMDDHHMMSS>-<microsecond-offset>-<8 chars of sha1(hostname -f)>-<pid>
There's obviously ways to make that more compact, but in this case I
couldn't see a reason to, also using UTC would be a good idea.
All the trace2 tests pass if I fake that up. Jeff H: Do you have
anything that relies on the current format?
> This makes it more convenient to collect traces for every git invocation
> by unconditionally setting the relevant trace2 envvar to a constant
> directory name.
>
> Signed-off-by: Josh Steadmon <stead...@google.com>
> ---
> Documentation/technical/api-trace2.txt | 5 ++
> t/t0210-trace2-normal.sh | 15 ++++++
> trace2/tr2_dst.c | 63 +++++++++++++++++++++++++-
> 3 files changed, 81 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/technical/api-trace2.txt
> b/Documentation/technical/api-trace2.txt
> index 2de565fa3d..d0948ba250 100644
> --- a/Documentation/technical/api-trace2.txt
> +++ b/Documentation/technical/api-trace2.txt
> @@ -109,6 +109,11 @@ values are recognized.
>
> Enables the target, opens and writes to the file in append mode.
>
> + If the target already exists and is a directory, the traces will be
> + written to files (one per process) underneath the given directory. They
> + will be named according to the last component of the SID (optionally
> + followed by a counter to avoid filename collisions).
> +
> `af_unix:[<socket_type>:]<absolute-pathname>`::
>
> Enables the target, opens and writes to a Unix Domain Socket
> diff --git a/t/t0210-trace2-normal.sh b/t/t0210-trace2-normal.sh
> index 03a0aedb1d..819430658b 100755
> --- a/t/t0210-trace2-normal.sh
> +++ b/t/t0210-trace2-normal.sh
> @@ -80,6 +80,21 @@ test_expect_success 'normal stream, return code 1' '
> test_cmp expect actual
> '
>
> +test_expect_success 'automatic filename' '
> + test_when_finished "rm -r traces actual expect" &&
> + mkdir traces &&
> + GIT_TR2="$(pwd)/traces" test-tool trace2 001return 0 &&
> + perl "$TEST_DIRECTORY/t0210/scrub_normal.perl" <"$(ls traces/*)"
> >actual &&
> + cat >expect <<-EOF &&
> + version $V
> + start _EXE_ trace2 001return 0
> + cmd_name trace2 (trace2)
> + exit elapsed:_TIME_ code:0
> + atexit elapsed:_TIME_ code:0
> + EOF
> + test_cmp expect actual
> +'
> +
> # Verb 002exit
> #
> # Explicit exit(code) from within cmd_<verb> propagates <code>.
> diff --git a/trace2/tr2_dst.c b/trace2/tr2_dst.c
> index fd490a43ad..c3d82ca6a4 100644
> --- a/trace2/tr2_dst.c
> +++ b/trace2/tr2_dst.c
> @@ -1,5 +1,6 @@
> #include "cache.h"
> #include "trace2/tr2_dst.h"
> +#include "trace2/tr2_sid.h"
>
> /*
> * If a Trace2 target cannot be opened for writing, we should issue a
> @@ -12,6 +13,11 @@
> */
> #define TR2_ENVVAR_DST_DEBUG "GIT_TR2_DST_DEBUG"
>
> +/*
> + * How many attempts we will make at creating an automatically-named trace
> file.
> + */
> +#define MAX_AUTO_ATTEMPTS 10
> +
> static int tr2_dst_want_warning(void)
> {
> static int tr2env_dst_debug = -1;
> @@ -36,6 +42,55 @@ void tr2_dst_trace_disable(struct tr2_dst *dst)
> dst->need_close = 0;
> }
>
> +static int tr2_dst_try_auto_path(struct tr2_dst *dst, const char *tgt_prefix)
> +{
> + int fd;
> + 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;
> +
> + 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);
> + }
> +
> + fd = open(path.buf, O_WRONLY | O_CREAT | O_EXCL, 0666);
> + if (fd != -1)
> + break;
> + }
> +
> + if (fd == -1) {
> + if (tr2_dst_want_warning())
> + warning("trace2: could not open '%.*s' for '%s'
> tracing: %s",
> + (int) base_path_len, path.buf,
> + dst->env_var_name, strerror(errno));
> +
> + tr2_dst_trace_disable(dst);
> + strbuf_release(&path);
> + return 0;
> + }
> +
> + strbuf_release(&path);
> +
> + dst->fd = fd;
> + 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);
> @@ -202,8 +257,12 @@ int tr2_dst_get_trace_fd(struct tr2_dst *dst)
> return dst->fd;
> }
>
> - if (is_absolute_path(tgt_value))
> - return tr2_dst_try_path(dst, tgt_value);
> + 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))
