the filesystem API should support sparse files for the call "get_file_map"

[korli]

the UDF filesystem uses sparse files (with blank chunks). The current API doesn't allow to describe such files. A proposed solution is to add a field "blank" to the struct file_io_vec for such blank chunks.

[korli]

I wouldn't call this an enhancement given the impact on the UDF filesystem, anyway ...

[wkornewald]

Hmm, I just found that bug doesn't fit (it's about extending the API), but feel free to change it to "bug". We'll need to define how we want to use Trac for release planning (what role do type and priority play, etc.) at some point.

[bonefish]

Adding at least read support for sparse files to the file cache (which would suffice for UDF) should require relatively few changes. It wouldn't even be necessary to add another field to file_io_vec; one could simply use a negative offset as indicator.

In fact the only two changes necessary should be to

• replace negative offsets by LONG_LONG_MIN in file_cache.cpp:get_file_map() and
• use a small wrapper for vfs_read_pages() which simply clears the pages in case of a negative offset.

[axeld]

Implemented in hrev28648. Sparse files report a disk offset of -1 for the sparse extents, read_file_io_vec_pages() will then zero them out.