On Tue, Jan 07, 2025 at 05:26:36PM -0800, Darrick J. Wong wrote: > "I think we should wire it up as a new FALLOC_FL_WRITE_ZEROES mode, > document very vigorously that it exists to facilitate pure overwrites > (specifically that it returns EOPNOTSUPP for always-cow files), and not > add more ioctls." > > If we added this new fallocate mode to set up written mappings, would it > be enough to write in the programming manuals that applications should > use it to prepare a file for block-untorn writes? Perhaps we should > change the errno code to EMEDIUMTYPE for the mixed mappings case. > > Alternately, maybe we /should/ let programs open a lease-fd on a file > range, do their untorn writes through the lease fd, and if another > thread does something to break the lease, then the lease fd returns EIO > until you close it. This still violates the "no unexpected errors" paradigm. The whole FALLOC_FL_WRITE_ZEROES (I hate that name btw) model would only work if we had a software fallback that make the operations slower but still work in case of an unexpected change to the extent mapping.
