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    SubjectRe: [PATCH v11 02/22] cachefiles: notify the user daemon when looking up cookie
    Date
    Jeffle Xu <jefflexu@linux.alibaba.com> 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@linux.alibaba.com>

    Acked-by: David Howells <dhowells@redhat.com>

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