git/connected.c
Derrick Stolee b739d971e5 connected.c: reprepare packs for corner cases
While updating the microsoft/git fork on top of v2.26.0-rc0 and
consuming that build into Scalar, I noticed a corner case bug around
partial clone.

The "scalar clone" command can create a Git repository with the
proper config for using partial clone with the "blob:none" filter.
Instead of calling "git clone", it runs "git init" then sets a few
more config values before running "git fetch".

In our builds on v2.26.0-rc0, we noticed that our "git fetch"
command was failing with

  error: https://github.com/microsoft/scalar did not send all necessary objects

This does not happen if you copy the config file from a repository
created by "git clone --filter=blob:none <url>", but it does happen
when adding the config option "core.logAllRefUpdates = true".

By debugging, I was able to see that the loop inside
check_connnected() that checks if all refs are contained in
promisor packs actually did not have any packfiles in the packed_git
list.

I'm not sure what corner-case issues caused this config option to
prevent the reprepare_packed_git() from being called at the proper
spot during the fetch operation. This approach requires a situation
where we use the remote helper process, which makes it difficult to
test.

It is possible to place a reprepare_packed_git() call in the fetch code
closer to where we receive a pack, but that leaves an opening for a
later change to re-introduce this problem. Further, a concurrent repack
operation could replace the pack-file list we already loaded into
memory, causing this issue in an even harder to reproduce scenario.

It is really the responsibility of anyone looping through the list of
pack-files for a certain object to fall back to reprepare_packed_git()
on a fail-to-find. The loop in check_connected() does not have this
fallback, leading to this bug.

We _could_ try looping through the packs and only reprepare the packs
after a miss, but that change is more involved and has little value.
Since this case is isolated to the case when
opt->check_refs_are_promisor_objects_only is true, we are confident that
we are verifying the refs after downloading new data. This implies that
calling reprepare_packed_git() in advance is not a huge cost compared to
the rest of the operations already made.

Helped-by: Jeff King <peff@peff.net>
Helped-by: Junio Hamano <gitster@pobox.com>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2020-03-15 15:39:00 -07:00

146 lines
4.2 KiB
C

#include "cache.h"
#include "object-store.h"
#include "run-command.h"
#include "sigchain.h"
#include "connected.h"
#include "transport.h"
#include "packfile.h"
#include "promisor-remote.h"
/*
* If we feed all the commits we want to verify to this command
*
* $ git rev-list --objects --stdin --not --all
*
* and if it does not error out, that means everything reachable from
* these commits locally exists and is connected to our existing refs.
* Note that this does _not_ validate the individual objects.
*
* Returns 0 if everything is connected, non-zero otherwise.
*/
int check_connected(oid_iterate_fn fn, void *cb_data,
struct check_connected_options *opt)
{
struct child_process rev_list = CHILD_PROCESS_INIT;
struct check_connected_options defaults = CHECK_CONNECTED_INIT;
char commit[GIT_MAX_HEXSZ + 1];
struct object_id oid;
int err = 0;
struct packed_git *new_pack = NULL;
struct transport *transport;
size_t base_len;
const unsigned hexsz = the_hash_algo->hexsz;
if (!opt)
opt = &defaults;
transport = opt->transport;
if (fn(cb_data, &oid)) {
if (opt->err_fd)
close(opt->err_fd);
return err;
}
if (transport && transport->smart_options &&
transport->smart_options->self_contained_and_connected &&
transport->pack_lockfile &&
strip_suffix(transport->pack_lockfile, ".keep", &base_len)) {
struct strbuf idx_file = STRBUF_INIT;
strbuf_add(&idx_file, transport->pack_lockfile, base_len);
strbuf_addstr(&idx_file, ".idx");
new_pack = add_packed_git(idx_file.buf, idx_file.len, 1);
strbuf_release(&idx_file);
}
if (opt->check_refs_are_promisor_objects_only) {
/*
* For partial clones, we don't want to have to do a regular
* connectivity check because we have to enumerate and exclude
* all promisor objects (slow), and then the connectivity check
* itself becomes a no-op because in a partial clone every
* object is a promisor object. Instead, just make sure we
* received, in a promisor packfile, the objects pointed to by
* each wanted ref.
*
* Before checking for promisor packs, be sure we have the
* latest pack-files loaded into memory.
*/
reprepare_packed_git(the_repository);
do {
struct packed_git *p;
for (p = get_all_packs(the_repository); p; p = p->next) {
if (!p->pack_promisor)
continue;
if (find_pack_entry_one(oid.hash, p))
goto promisor_pack_found;
}
return 1;
promisor_pack_found:
;
} while (!fn(cb_data, &oid));
return 0;
}
if (opt->shallow_file) {
argv_array_push(&rev_list.args, "--shallow-file");
argv_array_push(&rev_list.args, opt->shallow_file);
}
argv_array_push(&rev_list.args,"rev-list");
argv_array_push(&rev_list.args, "--objects");
argv_array_push(&rev_list.args, "--stdin");
if (has_promisor_remote())
argv_array_push(&rev_list.args, "--exclude-promisor-objects");
if (!opt->is_deepening_fetch) {
argv_array_push(&rev_list.args, "--not");
argv_array_push(&rev_list.args, "--all");
}
argv_array_push(&rev_list.args, "--quiet");
argv_array_push(&rev_list.args, "--alternate-refs");
if (opt->progress)
argv_array_pushf(&rev_list.args, "--progress=%s",
_("Checking connectivity"));
rev_list.git_cmd = 1;
rev_list.env = opt->env;
rev_list.in = -1;
rev_list.no_stdout = 1;
if (opt->err_fd)
rev_list.err = opt->err_fd;
else
rev_list.no_stderr = opt->quiet;
if (start_command(&rev_list))
return error(_("Could not run 'git rev-list'"));
sigchain_push(SIGPIPE, SIG_IGN);
commit[hexsz] = '\n';
do {
/*
* If index-pack already checked that:
* - there are no dangling pointers in the new pack
* - the pack is self contained
* Then if the updated ref is in the new pack, then we
* are sure the ref is good and not sending it to
* rev-list for verification.
*/
if (new_pack && find_pack_entry_one(oid.hash, new_pack))
continue;
memcpy(commit, oid_to_hex(&oid), hexsz);
if (write_in_full(rev_list.in, commit, hexsz + 1) < 0) {
if (errno != EPIPE && errno != EINVAL)
error_errno(_("failed write to rev-list"));
err = -1;
break;
}
} while (!fn(cb_data, &oid));
if (close(rev_list.in))
err = error_errno(_("failed to close rev-list's stdin"));
sigchain_pop(SIGPIPE);
return finish_command(&rev_list) || err;
}