tree a9b707976274a579422b776f7d68918e57863173
parent 190c882ce219ed89ac7d0633cfd11ad75fb0b46e
author Alexander Graf <agraf@suse.de> 1421935298 +0100
committer Juan Quintela <quintela@redhat.com> 1423152974 +0100

qemu-file: Add fast ftell code path

For ftell we flush the output buffer to ensure that we don't have anything
lingering in our internal buffers. This is a very safe thing to do.

However, with the dynamic size measurement that the dynamic vmstate
description will bring this would turn out quite slow.

Instead, we can fast path this specific measurement and just take the
internal buffers into account when telling the kernel our position.

I'm sure I overlooked some corner cases where this doesn't work, so
instead of tuning the safe, existing version, this patch adds a fast
variant of ftell that gets used by the dynamic vmstate description code
which isn't critical when it fails.

Signed-off-by: Alexander Graf <agraf@suse.de>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>