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    SubjectRe: [RFC PATCH 0/2] Union Mount: Directory listing in glibc
    In message <20080429133201.GA9938@localhost.localdomain>, bsn.0007@gmail.com writes:
    > Hi,
    >
    > I went through Bharata's RFC post on glibc based Union Mount readdir solution
    > (http://lkml.org/lkml/2008/3/11/34) and have come up with patches
    > against glibc to implement the same.
    [...]

    The last set of discussions on glibc support ended, as I understood it, with
    the glibc people objecting to such "special-purpose" code in glibc. See
    <http://lkml.org/lkml/2008/3/11/66>. So has anything changed behind the
    scenes, or is this idea unlikely to be merged into glibc any time soon, if
    ever. (Personally I'd love to rip out the readdir-related code from unionfs
    if glibc supported the same.)

    > Patch 1. readdir support for union mounted directories.
    > I am caching the dirent names in a list to aid duplicate elimination.
    > And this cache is stored in DIRP. For duplicate elimination I am using
    > strcmp(). I am not sure if this works universally with different types
    > of filesystems. Any suggestions here would be welcome.
    [...]

    You might consider using a hash table instead of a list; it'll be faster in
    case where there are a lot of whiteouts/duplicates to process.


    Also, I'll reiterate my previous concern that I think you may need to also
    handle "opaque directories". See the discussion in section 5.1 "Creation
    and deletion of whiteouts", in the original union mounts paper:

    <http://www.usenix.org/publications/library/proceedings/neworl/full_papers/mckusick.a>

    Cheers,
    Erez.


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