Sparse file handling to save space for ARM 64k binaries with small segments

[martinp26]

Hi,

I am observing that package builds for ARM64 that target compatibility with 64K PT kernels do lead to binaries and libraries with long zero runs as elf-files store all segments page aligned. In practice RPM does not have any sparse-file handling as of now. A quick test with sudo fallocate --dig-holes /bin/ln does reclaim space on such ARM distributions.

A typical distribution with many small binaries can easily waste 100+MB of disk storage when not using sparse files. (Using an advanced filesystem with compression would be another solution.)

I was thinking of adding sparseness detection in lib/rpmfi.c:rpmfiArchiveReadToFilePsm(). rpmlib would directly and transparently create sparse files on filesystems that support it for input files with non-trivial zero runs. Such a feature could be gated behind a %__sparse_install 0 macro so that it can be introduced gently.

I know that there were older attempts in a similar direction, but I am not seeing anything in the current code, issues or discussions. Current ARM64 trends might create new interest for this topic.

I have experimental patches, if there is interest.

[martinp26]

Something like this. The fallocate needs a little more discussion as it can positively influence fragmentation on xfs, but prevents compression on btrfs.

rpm4.16-sparse-install.patch