On Sat, Dec 25, 2010 at 12:33 PM, Nick Piggin <npiggin@xxxxxxxxx> wrote: >> It's not just about dpkg, I'm still very interested in answers to my >> original questions. > > Arbitrary atomic but non-durable file write operation? No, not arbitrary writes. It's about complete file writes. Also, don't forget my question about how to preserve meta-data including file owner. > That's significantly > different to how any part of the pagecache or filesystem or syscall API > is set up. Writes are not atomic, and syncs are only for durability (not > atomicity), atomicity is typically built on top of these durable points. > > That is quite fundamental functionality and suits simple > implementations of filesystems and writeback caches. > > If you start building complex atomicity semantics, then you get APIs Atomic semantics are not (that) complex. > which can't be supported by all filesystems, Linux specific, adds > complexity from the API through to the pagecache and to the > filesystems, and is Linux specific. > Compare that to using cross platform, mature and well tested sqlite > or bdb, how much reason do we have for implementing such APIs? Like I said before, it's not about DB-like functionality but about complete file writes/updates. For example, I've got a file in an editor and I want to save it. > It's not that it isn't possible, it's that there is no way we're adding > such a thing unless it really helps and is going to be widely used. > > What exact use case do you have in mind, and what exact API > semantics do you want, anyway? Let me copy the original post: Writing a temp file, fsync, rename is often proposed. However, the durable aspect of fsync isn't always required and this way has other issues, like losing file meta-data. What is the recommended way for atomic non-durable (complete) file writes? I'm also wondering why FSs commit after open/truncate but before write/close. AFAIK this isn't necessary and thus suboptimal. Olaf -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
