Re: pgsql: Logical Tape Set: lazily allocate read buffer.

Jeff Davis <jdavis(at)postgresql(dot)org> writes:
> Logical Tape Set: lazily allocate read buffer.

Coverity is not very pleased with this patch: it's spewing warnings like

1112 if (lt->buffer == NULL)
1113 ltsInitReadBuffer(lts, lt);
1114
1115 if (blocknum != lt->curBlockNumber)
1116 {
>>> CID 1458440: Null pointer dereferences (FORWARD_NULL)
>>> Passing null pointer "lt->buffer" to "ltsReadBlock", which dereferences it.
1117 ltsReadBlock(lts, blocknum, (void *) lt->buffer);
1118 lt->curBlockNumber = blocknum;

Evidently, it doesn't think that ltsInitReadBuffer() is guaranteed to
make lt->buffer not null, which is not so surprising considering
that that's coded this way:

if (lt->firstBlockNumber != -1L)
{
Assert(lt->buffer_size > 0);
lt->buffer = palloc(lt->buffer_size);
}

Is there a reason for that to be coded in such an obscure and fragile
fashion, rather than having the test be say "if (lt->buffer == NULL)"?
If we really need a connection to firstBlockNumber, I'd suggest
something like

- if (lt->firstBlockNumber != -1L)
+ if (lt->buffer == NULL)
{
+ Assert(lt->firstBlockNumber != -1L);
Assert(lt->buffer_size > 0);
lt->buffer = palloc(lt->buffer_size);
}

but I'm not sure the extra Assert has any value.

regards, tom lane