--- zzzz-none-000/linux-3.10.107/Documentation/filesystems/caching/netfs-api.txt 2017-06-27 09:49:32.000000000 +0000 +++ scorpion-7490-727/linux-3.10.107/Documentation/filesystems/caching/netfs-api.txt 2021-02-04 17:41:59.000000000 +0000 @@ -29,15 +29,16 @@ (6) Index registration (7) Data file registration (8) Miscellaneous object registration - (9) Setting the data file size + (9) Setting the data file size (10) Page alloc/read/write (11) Page uncaching - (12) Index and data file update - (13) Miscellaneous cookie operations - (14) Cookie unregistration - (15) Index invalidation - (16) Data file invalidation - (17) FS-Cache specific page flags. + (12) Index and data file consistency + (13) Cookie enablement + (14) Miscellaneous cookie operations + (15) Cookie unregistration + (16) Index invalidation + (17) Data file invalidation + (18) FS-Cache specific page flags. ============================= @@ -334,7 +335,8 @@ struct fscache_cookie * fscache_acquire_cookie(struct fscache_cookie *parent, const struct fscache_object_def *def, - void *netfs_data); + void *netfs_data, + bool enable); This function creates an index entry in the index represented by parent, filling in the index entry by calling the operations pointed to by def. @@ -350,6 +352,10 @@ may be created in several different caches independently at different times. This is all handled transparently, and the netfs doesn't see any of it. +A cookie will be created in the disabled state if enabled is false. A cookie +must be enabled to do anything with it. A disabled cookie can be enabled by +calling fscache_enable_cookie() (see below). + For example, with AFS, a cell would be added to the primary index. This index entry would have a dependent inode containing a volume location index for the volume mappings within this cell: @@ -357,7 +363,7 @@ cell->cache = fscache_acquire_cookie(afs_cache_netfs.primary_index, &afs_cell_cache_index_def, - cell); + cell, true); Then when a volume location was accessed, it would be entered into the cell's index and an inode would be allocated that acts as a volume type and hash chain @@ -366,7 +372,7 @@ vlocation->cache = fscache_acquire_cookie(cell->cache, &afs_vlocation_cache_index_def, - vlocation); + vlocation, true); And then a particular flavour of volume (R/O for example) could be added to that index, creating another index for vnodes (AFS inode equivalents): @@ -374,7 +380,7 @@ volume->cache = fscache_acquire_cookie(vlocation->cache, &afs_volume_cache_index_def, - volume); + volume, true); ====================== @@ -388,7 +394,7 @@ vnode->cache = fscache_acquire_cookie(volume->cache, &afs_vnode_cache_object_def, - vnode); + vnode, true); ================================= @@ -404,7 +410,7 @@ xattr->cache = fscache_acquire_cookie(vnode->cache, &afs_xattr_cache_object_def, - xattr); + xattr, true); Miscellaneous objects might be used to store extended attributes or directory entries for example. @@ -433,7 +439,7 @@ ===================== -PAGE READ/ALLOC/WRITE +PAGE ALLOC/READ/WRITE ===================== And the sixth step is to store and retrieve pages in the cache. There are @@ -499,7 +505,7 @@ (*) An argument that's 0 on success or negative for an error code. If an error occurs, it should be assumed that the page contains no usable - data. + data. fscache_readpages_cancel() may need to be called. end_io_func() will be called in process context if the read is results in an error, but it might be called in interrupt context if the read is @@ -623,6 +629,22 @@ been marked appropriately and will need uncaching. +CANCELLATION OF UNREAD PAGES +---------------------------- + +If one or more pages are passed to fscache_read_or_alloc_pages() but not then +read from the cache and also not read from the underlying filesystem then +those pages will need to have any marks and reservations removed. This can be +done by calling: + + void fscache_readpages_cancel(struct fscache_cookie *cookie, + struct list_head *pages); + +prior to returning to the caller. The cookie argument should be as passed to +fscache_read_or_alloc_pages(). Every page in the pages list will be examined +and any that have PG_fscache set will be uncached. + + ============== PAGE UNCACHING ============== @@ -690,9 +712,18 @@ error is returned. -========================== -INDEX AND DATA FILE UPDATE -========================== +=============================== +INDEX AND DATA FILE CONSISTENCY +=============================== + +To find out whether auxiliary data for an object is up to data within the +cache, the following function can be called: + + int fscache_check_consistency(struct fscache_cookie *cookie) + +This will call back to the netfs to check whether the auxiliary data associated +with a cookie is correct. It returns 0 if it is and -ESTALE if it isn't; it +may also return -ENOMEM and -ERESTARTSYS. To request an update of the index data for an index or other object, the following function should be called: @@ -708,6 +739,47 @@ data blocks are added to a data file object. +================= +COOKIE ENABLEMENT +================= + +Cookies exist in one of two states: enabled and disabled. If a cookie is +disabled, it ignores all attempts to acquire child cookies; check, update or +invalidate its state; allocate, read or write backing pages - though it is +still possible to uncache pages and relinquish the cookie. + +The initial enablement state is set by fscache_acquire_cookie(), but the cookie +can be enabled or disabled later. To disable a cookie, call: + + void fscache_disable_cookie(struct fscache_cookie *cookie, + bool invalidate); + +If the cookie is not already disabled, this locks the cookie against other +enable and disable ops, marks the cookie as being disabled, discards or +invalidates any backing objects and waits for cessation of activity on any +associated object before unlocking the cookie. + +All possible failures are handled internally. The caller should consider +calling fscache_uncache_all_inode_pages() afterwards to make sure all page +markings are cleared up. + +Cookies can be enabled or reenabled with: + + void fscache_enable_cookie(struct fscache_cookie *cookie, + bool (*can_enable)(void *data), + void *data) + +If the cookie is not already enabled, this locks the cookie against other +enable and disable ops, invokes can_enable() and, if the cookie is not an index +cookie, will begin the procedure of acquiring backing objects. + +The optional can_enable() function is passed the data argument and returns a +ruling as to whether or not enablement should actually be permitted to begin. + +All possible failures are handled internally. The cookie will only be marked +as enabled if provisional backing objects are allocated. + + =============================== MISCELLANEOUS COOKIE OPERATIONS =============================== @@ -753,7 +825,7 @@ To get rid of a cookie, this function should be called. void fscache_relinquish_cookie(struct fscache_cookie *cookie, - int retire); + bool retire); If retire is non-zero, then the object will be marked for recycling, and all copies of it will be removed from all active caches in which it is present.