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osd: refuse to return data payload if request wrote anything

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Write operations aren't allowed to return a data payload because
we can't do so reliably. If the client has to resend the request
and it has already been applied, we will return 0 with no
payload.  Non-deterministic behavior is no good.

See #1765.

Signed-off-by: Sage Weil <sage.weil@dreamhost.com>
This commit is contained in:
Sage Weil 2012-02-20 21:11:46 -08:00
parent d74e029406
commit 174f6b845c
1 changed files with 17 additions and 2 deletions
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19
src/osd/ReplicatedPG.cc
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@ -768,8 +768,23 @@ void ReplicatedPG::do_op(OpRequest *op)
// prepare the reply
ctx->reply = new MOSDOpReply(m, 0, get_osdmap()->get_epoch(), 0);
ctx->reply->claim_op_out_data(ctx->ops);
ctx->reply->get_header().data_off = ctx->data_off;
// Write operations aren't allowed to return a data payload because
// we can't do so reliably. If the client has to resend the request
// and it has already been applied, we will return 0 with no
// payload. Non-deterministic behavior is no good. However, it is
// possible to construct an operation that does a read, does a guard
// check (e.g., CMPXATTR), and then a write. Then we either succeed
// with the write, or return a CMPXATTR and the read value.
if (ctx->op_t.empty() && !ctx->modify) {
// read.
ctx->reply->claim_op_out_data(ctx->ops);
ctx->reply->get_header().data_off = ctx->data_off;
} else {
// write. normalize the result code.
if (result > 0)
result = 0;
}
ctx->reply->set_result(result);
if (result >= 0)