Jeffle Xu <jefflexu@xxxxxxxxxxxxxxxxx> wrote: > Fscache/CacheFiles used to serve as a local cache for a remote > networking fs. A new on-demand read mode will be introduced for > CacheFiles, which can boost the scenario where on-demand read semantics > are needed, e.g. container image distribution. > > The essential difference between these two modes is seen when a cache > miss occurs: In the original mode, the netfs will fetch the data from > the remote server and then write it to the cache file; in on-demand > read mode, fetching the data and writing it into the cache is delegated > to a user daemon. > > As the first step, notify the user daemon when looking up cookie. In > this case, an anonymous fd is sent to the user daemon, through which the > user daemon can write the fetched data to the cache file. Since the user > daemon may move the anonymous fd around, e.g. through dup(), an object > ID uniquely identifying the cache file is also attached. > > Also add one advisory flag (FSCACHE_ADV_WANT_CACHE_SIZE) suggesting that > the cache file size shall be retrieved at runtime. This helps the > scenario where one cache file contains multiple netfs files, e.g. for > the purpose of deduplication. In this case, netfs itself has no idea the > size of the cache file, whilst the user daemon should give the hint on > it. > > Signed-off-by: Jeffle Xu <jefflexu@xxxxxxxxxxxxxxxxx> Acked-by: David Howells <dhowells@xxxxxxxxxx>
