Hi Nick, sorry for my later reply, this has been on my to answer list for the last month and I only managed to get back to it now. On Thu, Feb 08, 2007 at 02:07:36PM +0100, Nick Piggin wrote: > Add a new "perform_write" aop, which replaces prepare_write and commit_write > as a single call to copy a given amount of userdata at the given offset. This > is more flexible, because the implementation can determine how to best handle > errors, or multi-page ranges (eg. it may use a gang lookup), and only requires > one call into the fs. I really like this idea, especially for avoiding to call into the allocator for every block. Have you contacted the reiser4 folks whether this would superceed their batch_write op completely? > One problem with this interface is that it cannot be used to write into the > filesystem by any means other than already-initialised buffers via iovecs. So > prepare/commit have to stay around for non-user data... Actually I think that's a a good thing to a certain extent. It reminds us that all other users are horrible abuse of the interface. I'd even go so far as to make batch_write a callback that the filesystem passes to generic_file_aio_write to make clear it's not a generic thing but a helper. (It's not a generic thing because it's the upper layer writing into the pagecache, not a pagecache to fs below operation). The still leaves open on how to get rid of ->prepare_write and ->commit_write compltely, and for that we'll probably need ->kernel_read and ->kernel_write file operations. But that's a step you shouldn't consider yet when doing this work. > Another thing is that it seems to be less able to be implemented in generic, > reusable code. It should be possible to introduce a new 2-op interface (or > maybe just a new error handler op) which can be used correctly in generic code. We should be able to find a nice abstraction for this, see my next mails. > + /* > + * perform_write replaces prepare and commit_write callbacks. > + */ This is a rather useless comment :) Better remove it and add a proper descriptions to Documentation/filesystems/vfs.txt and Documentation/filesystems/Locking - 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
