[$] Supporting untorn buffered writes

At last year's
Linux Storage, Filesystem,
Memory-Management, and BPF Summit (LSFMM+BPF), there was a discussion about atomic writes that was
accompanied by patches to support the feature in the block layer, and for
direct I/O on XFS. That
work was merged, but another piece of that discussion concerned adding the
feature for buffered I/O, in part because the PostgreSQL database currently
has to jump through hoops to ensure that its writes are not 'torn'
(partially written) when there is an error or crash. Luis Chamberlain led
a combined storage and filesystem track at this year's summit to revisit
the idea of providing atomic (or untorn) writes for buffered I/O.