I am working a bit with sparse files, and I need to output the list of holes in my file. To my great surprise, I found that my file had more holes than I put...

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Sparse files save disk space by storing only non-zero data blocks, with zero-filled regions recorded as metadata. When using fallocate() to reserve disk space, the allocated regions are marked as 'unwritten' by the filesystem, which lseek(SEEK_HOLE) treats as holes even though space is physically allocated. This optimization avoids unnecessary I/O by returning zeros directly without reading from disk. The ioctl(FS_IOC_FIEMAP) system call can distinguish between true sparse holes and unwritten allocated regions.

The hole in my falloaction