• Jeffle Xu's avatar
    cachefiles: notify the user daemon when looking up cookie · c8383054
    Jeffle Xu authored
    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: default avatarJeffle Xu <jefflexu@linux.alibaba.com>
    Link: https://lore.kernel.org/r/20220509074028.74954-3-jefflexu@linux.alibaba.comAcked-by: default avatarDavid Howells <dhowells@redhat.com>
    Signed-off-by: default avatarGao Xiang <hsiangkao@linux.alibaba.com>
    c8383054
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