• David Howells's avatar
    FS-Cache: Implement data I/O part of netfs API · b5108822
    David Howells authored
    Implement the data I/O part of the FS-Cache netfs API.  The documentation and
    API header file were added in a previous patch.
    
    This patch implements the following functions for the netfs to call:
    
     (*) fscache_attr_changed().
    
         Indicate that the object has changed its attributes.  The only attribute
         currently recorded is the file size.  Only pages within the set file size
         will be stored in the cache.
    
         This operation is submitted for asynchronous processing, and will return
         immediately.  It will return -ENOMEM if an out of memory error is
         encountered, -ENOBUFS if the object is not actually cached, or 0 if the
         operation is successfully queued.
    
     (*) fscache_read_or_alloc_page().
     (*) fscache_read_or_alloc_pages().
    
         Request data be fetched from the disk, and allocate internal metadata to
         track the netfs pages and reserve disk space for unknown pages.
    
         These operations perform semi-asynchronous data reads.  Upon returning
         they will indicate which pages they think can be retrieved from disk, and
         will have set in progress attempts to retrieve those pages.
    
         These will return, in order of preference, -ENOMEM on memory allocation
         error, -ERESTARTSYS if a signal interrupted proceedings, -ENODATA if one
         or more requested pages are not yet cached, -ENOBUFS if the object is not
         actually cached or if there isn't space for future pages to be cached on
         this object, or 0 if successful.
    
         In the case of the multipage function, the pages for which reads are set
         in progress will be removed from the list and the page count decreased
         appropriately.
    
         If any read operations should fail, the completion function will be given
         an error, and will also be passed contextual information to allow the
         netfs to fall back to querying the server for the absent pages.
    
         For each successful read, the page completion function will also be
         called.
    
         Any pages subsequently tracked by the cache will have PG_fscache set upon
         them on return.  fscache_uncache_page() must be called for such pages.
    
         If supplied by the netfs, the mark_pages_cached() cookie op will be
         invoked for any pages now tracked.
    
     (*) fscache_alloc_page().
    
         Allocate internal metadata to track a netfs page and reserve disk space.
    
         This will return -ENOMEM on memory allocation error, -ERESTARTSYS on
         signal, -ENOBUFS if the object isn't cached, or there isn't enough space
         in the cache, or 0 if successful.
    
         Any pages subsequently tracked by the cache will have PG_fscache set upon
         them on return.  fscache_uncache_page() must be called for such pages.
    
         If supplied by the netfs, the mark_pages_cached() cookie op will be
         invoked for any pages now tracked.
    
     (*) fscache_write_page().
    
         Request data be stored to disk.  This may only be called on pages that
         have been read or alloc'd by the above three functions and have not yet
         been uncached.
    
         This will return -ENOMEM on memory allocation error, -ERESTARTSYS on
         signal, -ENOBUFS if the object isn't cached, or there isn't immediately
         enough space in the cache, or 0 if successful.
    
         On a successful return, this operation will have queued the page for
         asynchronous writing to the cache.  The page will be returned with
         PG_fscache_write set until the write completes one way or another.  The
         caller will not be notified if the write fails due to an I/O error.  If
         that happens, the object will become available and all pending writes will
         be aborted.
    
         Note that the cache may batch up page writes, and so it may take a while
         to get around to writing them out.
    
         The caller must assume that until PG_fscache_write is cleared the page is
         use by the cache.  Any changes made to the page may be reflected on disk.
         The page may even be under DMA.
    
     (*) fscache_uncache_page().
    
         Indicate that the cache should stop tracking a page previously read or
         alloc'd from the cache.  If the page was alloc'd only, but unwritten, it
         will not appear on disk.
    Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
    Acked-by: default avatarSteve Dickson <steved@redhat.com>
    Acked-by: default avatarTrond Myklebust <Trond.Myklebust@netapp.com>
    Acked-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
    Tested-by: default avatarDaire Byrne <Daire.Byrne@framestore.com>
    b5108822
page.c 20.7 KB