[PhilipRoman]

Yeah there are, Linux supports parameters FALLOC_FL_INSERT_RANGE and FALLOC_FL_COLLAPSE_RANGE for fallocate(2). Like most fancy filesystem features, they are not used by the vast majority of software because it has to run on any filesystem so you'd always need to maintain two implementations (and extensive test cases).

[cubefox]

Interesting that after decades of file system history, this is still considered a "fancy feature", considering that editing files is a pretty basic operation for a file system. Though I assume there are reasons why this hasn't become standard long ago.

[layer8]

File systems aren’t databases; they manage flat files, not structured data. You also can’t just insert/remove random amounts of bytes in RAM. The considerations here are actually quite similar, like fragmentation. If you make a hundred small edits to a file, you might end up with the file taking up ten times as much space due to fragmentation, and then you’d need the file system to do some sort of defragmentation pass to rewrite the file more contiguously again.

In addition, it’s generally nontrivial for a program to map changes to an in-memory object structure back to surgical edits of a flat file. It’s much easier to always just serialize the whole thing, or if the file format allows it, appending the serialized changes to the file.

[altfredd]

They are fully supported almost everywhere. XFS, ext4, tmpfs, f2fs and a bunch of misc filesystems all support them.

Ext4 support dates as early as Linux 3.15, released in 2014. It is ancient at this point!

[formerly_proven]

What this does on typical extent-based file systems is split the extent of the file at the given location (which means these operations can only be done with cluster granularity) and then insert a third extent. i.e. calling INSERT_RANGE once will give you a file with at least three extents (fragments). This, plus the mkfs-options-dependent alignment requirements, makes it really quite uninteresting for broad use in a similar fashion as O_DIRECT is uninteresting.

[cubefox]

Well, better an uninteresting solution than a solution which is actively terrible: appending changes to a PDF, which will inflate its size and cause data leakage.