[Libguestfs] [PATCH nbdkit v2 0/4] curl: Use a curl handle pool

[Richard W.M. Jones]

NOTE! At least patch 4 should not be applied, and maybe the whole
series is a bust.  I am mainly posting this on the list for discussion
and maybe to archive it.

Version 1 was here:
https://listman.redhat.com/archives/libguestfs/2023-February/030610.html

This patch series introduces the concept of a pool of libcurl handles,
instead of always associating one libcurl handle with one NBD
connection.  This gives you a bit more flexibility, eg. you can have a
highly concurrent multi-conn NBD connection, but not overwhelm the
remote web server with HTTP connections.  Or vice versa.

Compared to the earlier version, I have pushed a couple of simple
patches from the old series upstream.  The remaining patches are
tidied up a bit and better tested, but are largely the same.

Patches 1-3 on their own are performance neutral in the cases I tested
where you have approximately the same number of NBD connections as web
server connections (as expected).

Patch 4 kills performance, for reasons discussed here:
https://listman.redhat.com/archives/libguestfs/2023-February/030618.html
I was not able to fix this although I have tried several approaches.

Rich.