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git/ls-refs.c
Jacob Vosmaer 70afef5cdf upload-pack: use stdio in send_ref callbacks
In both protocol v0 and v2, upload-pack writes one pktline packet per
advertised ref to stdout. That means one or two write(2) syscalls per
ref. This is problematic if these writes become network sends with
high overhead.

This commit changes both send_ref callbacks to use buffered IO using
stdio.

To give an example of the impact: I set up a single-threaded loop that
calls ls-remote (with HTTP and protocol v2) on a local GitLab
instance, on a repository with 11K refs. When I switch from Git
v2.32.0 to this patch, I see a 40% reduction in CPU time for Git, and
65% for Gitaly (GitLab's Git RPC service).

So using buffered IO not only saves syscalls in upload-pack, it also
saves time in things that consume upload-pack's output.

Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Jacob Vosmaer <jacob@gitlab.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2021-09-01 10:20:39 -07:00

189 lines
4.4 KiB
C

#include "cache.h"
#include "repository.h"
#include "refs.h"
#include "remote.h"
#include "strvec.h"
#include "ls-refs.h"
#include "pkt-line.h"
#include "config.h"
static int config_read;
static int advertise_unborn;
static int allow_unborn;
static void ensure_config_read(void)
{
const char *str = NULL;
if (config_read)
return;
if (repo_config_get_string_tmp(the_repository, "lsrefs.unborn", &str)) {
/*
* If there is no such config, advertise and allow it by
* default.
*/
advertise_unborn = 1;
allow_unborn = 1;
} else {
if (!strcmp(str, "advertise")) {
advertise_unborn = 1;
allow_unborn = 1;
} else if (!strcmp(str, "allow")) {
allow_unborn = 1;
} else if (!strcmp(str, "ignore")) {
/* do nothing */
} else {
die(_("invalid value '%s' for lsrefs.unborn"), str);
}
}
config_read = 1;
}
/*
* Check if one of the prefixes is a prefix of the ref.
* If no prefixes were provided, all refs match.
*/
static int ref_match(const struct strvec *prefixes, const char *refname)
{
int i;
if (!prefixes->nr)
return 1; /* no restriction */
for (i = 0; i < prefixes->nr; i++) {
const char *prefix = prefixes->v[i];
if (starts_with(refname, prefix))
return 1;
}
return 0;
}
struct ls_refs_data {
unsigned peel;
unsigned symrefs;
struct strvec prefixes;
unsigned unborn : 1;
};
static int send_ref(const char *refname, const struct object_id *oid,
int flag, void *cb_data)
{
struct ls_refs_data *data = cb_data;
const char *refname_nons = strip_namespace(refname);
struct strbuf refline = STRBUF_INIT;
if (ref_is_hidden(refname_nons, refname))
return 0;
if (!ref_match(&data->prefixes, refname_nons))
return 0;
if (oid)
strbuf_addf(&refline, "%s %s", oid_to_hex(oid), refname_nons);
else
strbuf_addf(&refline, "unborn %s", refname_nons);
if (data->symrefs && flag & REF_ISSYMREF) {
struct object_id unused;
const char *symref_target = resolve_ref_unsafe(refname, 0,
&unused,
&flag);
if (!symref_target)
die("'%s' is a symref but it is not?", refname);
strbuf_addf(&refline, " symref-target:%s",
strip_namespace(symref_target));
}
if (data->peel && oid) {
struct object_id peeled;
if (!peel_iterated_oid(oid, &peeled))
strbuf_addf(&refline, " peeled:%s", oid_to_hex(&peeled));
}
strbuf_addch(&refline, '\n');
packet_fwrite(stdout, refline.buf, refline.len);
strbuf_release(&refline);
return 0;
}
static void send_possibly_unborn_head(struct ls_refs_data *data)
{
struct strbuf namespaced = STRBUF_INIT;
struct object_id oid;
int flag;
int oid_is_null;
strbuf_addf(&namespaced, "%sHEAD", get_git_namespace());
if (!resolve_ref_unsafe(namespaced.buf, 0, &oid, &flag))
return; /* bad ref */
oid_is_null = is_null_oid(&oid);
if (!oid_is_null ||
(data->unborn && data->symrefs && (flag & REF_ISSYMREF)))
send_ref(namespaced.buf, oid_is_null ? NULL : &oid, flag, data);
strbuf_release(&namespaced);
}
static int ls_refs_config(const char *var, const char *value, void *data)
{
/*
* We only serve fetches over v2 for now, so respect only "uploadpack"
* config. This may need to eventually be expanded to "receive", but we
* don't yet know how that information will be passed to ls-refs.
*/
return parse_hide_refs_config(var, value, "uploadpack");
}
int ls_refs(struct repository *r, struct strvec *keys,
struct packet_reader *request)
{
struct ls_refs_data data;
memset(&data, 0, sizeof(data));
strvec_init(&data.prefixes);
ensure_config_read();
git_config(ls_refs_config, NULL);
while (packet_reader_read(request) == PACKET_READ_NORMAL) {
const char *arg = request->line;
const char *out;
if (!strcmp("peel", arg))
data.peel = 1;
else if (!strcmp("symrefs", arg))
data.symrefs = 1;
else if (skip_prefix(arg, "ref-prefix ", &out))
strvec_push(&data.prefixes, out);
else if (!strcmp("unborn", arg))
data.unborn = allow_unborn;
}
if (request->status != PACKET_READ_FLUSH)
die(_("expected flush after ls-refs arguments"));
send_possibly_unborn_head(&data);
if (!data.prefixes.nr)
strvec_push(&data.prefixes, "");
for_each_fullref_in_prefixes(get_git_namespace(), data.prefixes.v,
send_ref, &data, 0);
packet_fflush(stdout);
strvec_clear(&data.prefixes);
return 0;
}
int ls_refs_advertise(struct repository *r, struct strbuf *value)
{
if (value) {
ensure_config_read();
if (advertise_unborn)
strbuf_addstr(value, "unborn");
}
return 1;
}