xen-tools: Reduce the number of string reallocations in QEMU

[temerkhanov]

Signed-off-by: Sergey Temerkhanov [email protected]

[temerkhanov]

While this seems reasonable @temerkhanov -- I wonder why do you think we need it -- IOW what's the improvement with this PR.

Have you seen this function in a profiling of some kind (perf, VTune, etc.) sticking out from the rest somehow?

Yes, both pprof and VTune were pointing at it for constant memory reallocation. That is a costly operation in terms of CPU time either

[rouming]

@eriknordmark can we close this? There is no perf numbers, nothing. The function local_open_nofollow() (the aim of this change) is called on attempt to open, readlink, truncate and statfs calls inside the 9p fs driver. I really doubt there is any file manipulations while guest is running, this is not a hot IO path.

[eriknordmark]

Closed based on @rouming's analysis.