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libcriu: add single pre-dump support

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In contrast to the CLI it is not possible to do a single pre-dump via
RPC and thus libcriu. In cr-service.c pre-dump always goes into a
pre-dump loop followed by a final dump. runc already works around this
to only do a single pre-dump by killing the CRIU process waiting for the
message for the final dump.

Trying to implement pre-dump in crun via libcriu it is not as easy to
work around CRIU's pre-dump loop expectations as with runc that directly
talks to CRIU via RPC.

We know that LXC/LXD also does single pre-dumps using the CLI and runc
also only does single pre-dumps by misusing the pre-dump loop interface.

With this commit it is possible to trigger a single pre-dump via RPC and
libcriu without misusing the interface provided via cr-service.c. So
this commit basically updates CRIU to the existing use cases.

The existing pre-dump loop still sounds like a very good idea, but so
far most tools have decided to implement the pre-dump loop themselves.

With this change we can implement pre-dump in crun to match what is
currently implemented in runc.

Signed-off-by: Adrian Reber <areber@redhat.com>
This commit is contained in:
Adrian Reber
2021-12-03 14:32:33 +00:00
committed by Andrei Vagin
parent 119a798856
commit 51a1adbc03
4 changed files with 30 additions and 8 deletions
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21
lib/c/criu.c
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@@ -1527,7 +1527,7 @@ int criu_check(void)
return criu_local_check(global_opts);
}
int criu_local_dump(criu_opts *opts)
static int dump(bool pre_dump, criu_opts *opts)
{
int ret = -1;
CriuReq req = CRIU_REQ__INIT;
@@ -1535,7 +1535,7 @@ int criu_local_dump(criu_opts *opts)
saved_errno = 0;
req.type = CRIU_REQ_TYPE__DUMP;
req.type = pre_dump ? CRIU_REQ_TYPE__SINGLE_PRE_DUMP : CRIU_REQ_TYPE__DUMP;
req.opts = opts->rpc;
ret = send_req_and_recv_resp(opts, &req, &resp);
@@ -1543,7 +1543,7 @@ int criu_local_dump(criu_opts *opts)
goto exit;
if (resp->success) {
if (resp->dump->has_restored && resp->dump->restored)
if (!pre_dump && resp->dump->has_restored && resp->dump->restored)
ret = 1;
else
ret = 0;
@@ -1561,11 +1561,26 @@ exit:
return ret;
}
int criu_local_dump(criu_opts *opts)
{
return dump(false, opts);
}
int criu_dump(void)
{
return criu_local_dump(global_opts);
}
int criu_local_pre_dump(criu_opts *opts)
{
return dump(true, opts);
}
int criu_pre_dump(void)
{
return criu_local_pre_dump(global_opts);
}
int criu_local_dump_iters(criu_opts *opts, int (*more)(criu_predump_info pi))
{
int ret = -1, fd = -1, uret;