• David Howells's avatar
    afs: Overhaul permit caching · be080a6f
    David Howells authored
    Overhaul permit caching in AFS by making it per-vnode and sharing permit
    lists where possible.
    
    When most of the fileserver operations are called, they return a status
    structure indicating the (revised) details of the vnode or vnodes involved
    in the operation.  This includes the access mark derived from the ACL
    (named CallerAccess in the protocol definition file).  This is cacheable
    and if the ACL changes, the server will tell us that it is breaking the
    callback promise, at which point we can discard the currently cached
    permits.
    
    With this patch, the afs_permits structure has, at the end, an array of
    { key, CallerAccess } elements, sorted by key pointer.  This is then cached
    in a hash table so that it can be shared between vnodes with the same
    access permits.
    
    Permit lists can only be shared if they contain the exact same set of
    key->CallerAccess mappings.
    
    Note that that table is global rather than being per-net_ns.  If the keys
    in a permit list cross net_ns boundaries, there is no problem sharing the
    cached permits, since the permits are just integer masks.
    
    Since permit lists pin keys, the permit cache also makes it easier for a
    future patch to find all occurrences of a key and remove them by means of
    setting the afs_permits::invalidated flag and then clearing the appropriate
    key pointer.  In such an event, memory barriers will need adding.
    
    Lastly, the permit caching is skipped if the server has sent either a
    vnode-specific or an entire-server callback since the start of the
    operation.
    Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
    be080a6f
internal.h 32.4 KB