[Buildroot] [PATCH 4/4] pkg-download: check hasahes for locally cached files

Peter Korsgaard peter at korsgaard.com
Tue Dec 2 09:27:05 UTC 2014

>>>>> "Thomas" == Thomas Petazzoni <thomas.petazzoni at free-electrons.com> writes:


>> So, to avoid this situation, check the hashes prior to doing the
 >> download. If the hashes match, consider the locally cached file genuine,
 >> and do not download it. However, if the locally cached file does not
 >> match the known hashes we have for it, it is promptly removed, and a
 >> download is re-attempted.

 > So in essence, from now on, at each build, we are re-checking the
 > hashes, while previously they were checked only when the file was
 > downloaded. Not that great for build time, but well, again maybe the
 > time to check the hashes is negligible compared to the build time. And
 > we can assume that a big tarball, which takes a certain time to hash,
 > will also contain a lot of source code to build, so the time to
 > calculate the hash is proportional to the build time of the package. So
 > if you're ready to spend several minutes to build Qt, you're probably
 > ready to wait a few more seconds to calculate the hash of the Qt
 > tarball each time.

I doubt it adds any significant time. Probably the hash and extract
steps are largely I/O bound, so "pre-heating" the page cache by
calculating a hash on the tarball before extracting it shouldn't matter

Bye, Peter Korsgaard

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