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Merge tag 'fscache-next-20180406' of git://git.kernel.org/pub/scm/lin…
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…ux/kernel/git/dhowells/linux-fs

Pull fscache updates from David Howells:
 "Three patches that fix some of AFS's usage of fscache:

   (1) Need to invalidate the cache if a foreign data change is detected
       on the server.

   (2) Move the vnode ID uniquifier (equivalent to i_generation) from
       the auxiliary data to the index key to prevent a race between
       file delete and a subsequent file create seeing the same index
       key.

   (3) Need to retire cookies that correspond to files that we think got
       deleted on the server.

  Four patches to fix some things in fscache and cachefiles:

   (4) Fix a couple of checker warnings.

   (5) Correctly indicate to the end-of-operation callback whether an
       operation completed or was cancelled.

   (6) Add a check for multiple cookie relinquishment.

   (7) Fix a path through the asynchronous write that doesn't wake up a
       waiter for a page if the cache decides not to write that page,
       but discards it instead.

  A couple of patches to add tracepoints to fscache and cachefiles:

   (8) Add tracepoints for cookie operators, object state machine
       execution, cachefiles object management and cachefiles VFS
       operations.

   (9) Add tracepoints for fscache operation management and page
       wrangling.

  And then three development patches:

  (10) Attach the index key and auxiliary data to the cookie, pass this
       information through various fscache-netfs API functions and get
       rid of the callbacks to the netfs to get it.

       This means that the cache can get at this information, even if
       the netfs goes away. It also means that the cache can be lazy in
       updating the coherency data.

  (11) Pass the object data size through various fscache-netfs API
       rather than calling back to the netfs for it, and store the value
       in the object.

       This makes it easier to correctly resize the object, as the size
       is updated on writes to the cache, rather than calling back out
       to the netfs.

  (12) Maintain a catalogue of allocated cookies. This makes it possible
       to catch cookie collision up front rather than down in the bowels
       of the cache being run from a service thread from the object
       state machine.

       This will also make it possible in the future to reconnect to a
       cookie that's not gone dead yet because it's waiting for
       finalisation of the storage and also make it possible to bring
       cookies online if the cache is added after the cookie has been
       obtained"

* tag 'fscache-next-20180406' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs:
  fscache: Maintain a catalogue of allocated cookies
  fscache: Pass object size in rather than calling back for it
  fscache: Attach the index key and aux data to the cookie
  fscache: Add more tracepoints
  fscache: Add tracepoints
  fscache: Fix hanging wait on page discarded by writeback
  fscache: Detect multiple relinquishment of a cookie
  fscache: Pass the correct cancelled indications to fscache_op_complete()
  fscache, cachefiles: Fix checker warnings
  afs: Be more aggressive in retiring cached vnodes
  afs: Use the vnode ID uniquifier in the cache key not the aux data
  afs: Invalidate cache on server data change
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torvalds committed Apr 7, 2018
2 parents f605ba9 + ec0328e commit 62f8e6c
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157 changes: 77 additions & 80 deletions Documentation/filesystems/caching/netfs-api.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -129,20 +129,10 @@ To define an object, a structure of the following type should be filled out:
const void *parent_netfs_data,
const void *cookie_netfs_data);

uint16_t (*get_key)(const void *cookie_netfs_data,
void *buffer,
uint16_t bufmax);

void (*get_attr)(const void *cookie_netfs_data,
uint64_t *size);

uint16_t (*get_aux)(const void *cookie_netfs_data,
void *buffer,
uint16_t bufmax);

enum fscache_checkaux (*check_aux)(void *cookie_netfs_data,
const void *data,
uint16_t datalen);
uint16_t datalen,
loff_t object_size);

void (*get_context)(void *cookie_netfs_data, void *context);

Expand Down Expand Up @@ -187,36 +177,7 @@ This has the following fields:
cache in the parent's list will be chosen, or failing that, the first
cache in the master list.

(4) A function to retrieve an object's key from the netfs [mandatory].

This function will be called with the netfs data that was passed to the
cookie acquisition function and the maximum length of key data that it may
provide. It should write the required key data into the given buffer and
return the quantity it wrote.

(5) A function to retrieve attribute data from the netfs [optional].

This function will be called with the netfs data that was passed to the
cookie acquisition function. It should return the size of the file if
this is a data file. The size may be used to govern how much cache must
be reserved for this file in the cache.

If the function is absent, a file size of 0 is assumed.

(6) A function to retrieve auxiliary data from the netfs [optional].

This function will be called with the netfs data that was passed to the
cookie acquisition function and the maximum length of auxiliary data that
it may provide. It should write the auxiliary data into the given buffer
and return the quantity it wrote.

If this function is absent, the auxiliary data length will be set to 0.

The length of the auxiliary data buffer may be dependent on the key
length. A netfs mustn't rely on being able to provide more than 400 bytes
for both.

(7) A function to check the auxiliary data [optional].
(4) A function to check the auxiliary data [optional].

This function will be called to check that a match found in the cache for
this object is valid. For instance with AFS it could check the auxiliary
Expand All @@ -226,6 +187,9 @@ This has the following fields:
If this function is absent, it will be assumed that matching objects in a
cache are always valid.

The function is also passed the cache's idea of the object size and may
use this to manage coherency also.

If present, the function should return one of the following values:

(*) FSCACHE_CHECKAUX_OKAY - the entry is okay as is
Expand All @@ -235,7 +199,7 @@ This has the following fields:
This function can also be used to extract data from the auxiliary data in
the cache and copy it into the netfs's structures.

(8) A pair of functions to manage contexts for the completion callback
(5) A pair of functions to manage contexts for the completion callback
[optional].

The cache read/write functions are passed a context which is then passed
Expand All @@ -249,7 +213,7 @@ This has the following fields:
required for indices as indices may not contain data. These functions may
be called in interrupt context and so may not sleep.

(9) A function to mark a page as retaining cache metadata [optional].
(6) A function to mark a page as retaining cache metadata [optional].

This is called by the cache to indicate that it is retaining in-memory
information for this page and that the netfs should uncache the page when
Expand All @@ -261,7 +225,7 @@ This has the following fields:

This function is not required for indices as they're not permitted data.

(10) A function to unmark all the pages retaining cache metadata [mandatory].
(7) A function to unmark all the pages retaining cache metadata [mandatory].

This is called by FS-Cache to indicate that a backing store is being
unbound from a cookie and that all the marks on the pages should be
Expand Down Expand Up @@ -333,12 +297,32 @@ the path to the file:
struct fscache_cookie *
fscache_acquire_cookie(struct fscache_cookie *parent,
const struct fscache_object_def *def,
const void *index_key,
size_t index_key_len,
const void *aux_data,
size_t aux_data_len,
void *netfs_data,
loff_t object_size,
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.

A unique key that represents the object within the parent must be pointed to by
index_key and is of length index_key_len.

An optional blob of auxiliary data that is to be stored within the cache can be
pointed to with aux_data and should be of length aux_data_len. This would
typically be used for storing coherency data.

The netfs may pass an arbitrary value in netfs_data and this will be presented
to it in the event of any calling back. This may also be used in tracing or
logging of messages.

The cache tracks the size of the data attached to an object and this set to be
object_size. For indices, this should be 0. This value will be passed to the
->check_aux() callback.

Note that this function never returns an error - all errors are handled
internally. It may, however, return NULL to indicate no cookie. It is quite
acceptable to pass this token back to this function as the parent to another
Expand All @@ -355,30 +339,24 @@ 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:
entry would have a dependent inode containing volume mappings within this cell:

cell->cache =
fscache_acquire_cookie(afs_cache_netfs.primary_index,
&afs_cell_cache_index_def,
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
combination:
cell->name, strlen(cell->name),
NULL, 0,
cell, 0, true);

vlocation->cache =
fscache_acquire_cookie(cell->cache,
&afs_vlocation_cache_index_def,
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):
And then a particular volume could be added to that index by ID, creating
another index for vnodes (AFS inode equivalents):

volume->cache =
fscache_acquire_cookie(vlocation->cache,
fscache_acquire_cookie(volume->cell->cache,
&afs_volume_cache_index_def,
volume, true);
&volume->vid, sizeof(volume->vid),
NULL, 0,
volume, 0, true);


======================
Expand All @@ -392,7 +370,9 @@ the object definition should be something other than index type.
vnode->cache =
fscache_acquire_cookie(volume->cache,
&afs_vnode_cache_object_def,
vnode, true);
&key, sizeof(key),
&aux, sizeof(aux),
vnode, vnode->status.size, true);


=================================
Expand All @@ -408,7 +388,9 @@ it would be some other type of object such as a data file.
xattr->cache =
fscache_acquire_cookie(vnode->cache,
&afs_xattr_cache_object_def,
xattr, true);
&xattr->name, strlen(xattr->name),
NULL, 0,
xattr, strlen(xattr->val), true);

Miscellaneous objects might be used to store extended attributes or directory
entries for example.
Expand All @@ -425,8 +407,7 @@ cache to adjust its metadata for data tracking appropriately:
int fscache_attr_changed(struct fscache_cookie *cookie);

The cache will return -ENOBUFS if there is no backing cache or if there is no
space to allocate any extra metadata required in the cache. The attributes
will be accessed with the get_attr() cookie definition operation.
space to allocate any extra metadata required in the cache.

Note that attempts to read or write data pages in the cache over this size may
be rebuffed with -ENOBUFS.
Expand Down Expand Up @@ -551,12 +532,13 @@ written back to the cache:

int fscache_write_page(struct fscache_cookie *cookie,
struct page *page,
loff_t object_size,
gfp_t gfp);

The cookie argument must specify a data file cookie, the page specified should
contain the data to be written (and is also used to specify the page number),
and the gfp argument is used to control how any memory allocations made are
satisfied.
object_size is the revised size of the object and the gfp argument is used to
control how any memory allocations made are satisfied.

The page must have first been read or allocated successfully and must not have
been uncached before writing is performed.
Expand Down Expand Up @@ -717,21 +699,23 @@ 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)
int fscache_check_consistency(struct fscache_cookie *cookie,
const void *aux_data);

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.
with a cookie is correct; if aux_data is non-NULL, it will update the auxiliary
data buffer first. 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:

void fscache_update_cookie(struct fscache_cookie *cookie);
void fscache_update_cookie(struct fscache_cookie *cookie,
const void *aux_data);

This function will refer back to the netfs_data pointer stored in the cookie by
the acquisition function to obtain the data to write into each revised index
entry. The update method in the parent index definition will be called to
transfer the data.
This function will update the cookie's auxiliary data buffer from aux_data if
that is non-NULL and then schedule this to be stored on disk. The update
method in the parent index definition will be called to transfer the data.

Note that partial updates may happen automatically at other times, such as when
data blocks are added to a data file object.
Expand All @@ -748,10 +732,11 @@ 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,
const void *aux_data,
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
Expand All @@ -760,13 +745,15 @@ 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,
const void *aux_data,
loff_t object_size,
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.
Expand All @@ -777,6 +764,12 @@ 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.

The object's data size is updated from object_size and is passed to the
->check_aux() function.

In both cases, the cookie's auxiliary data buffer is updated from aux_data if
that is non-NULL inside the enablement lock before proceeding.


===============================
MISCELLANEOUS COOKIE OPERATIONS
Expand Down Expand Up @@ -823,6 +816,7 @@ COOKIE UNREGISTRATION
To get rid of a cookie, this function should be called.

void fscache_relinquish_cookie(struct fscache_cookie *cookie,
const void *aux_data,
bool retire);

If retire is non-zero, then the object will be marked for recycling, and all
Expand All @@ -833,6 +827,9 @@ If retire is zero, then the object may be available again when next the
acquisition function is called. Retirement here will overrule the pinning on a
cookie.

The cookie's auxiliary data will be updated from aux_data if that is non-NULL
so that the cache can lazily update it on disk.

One very important note - relinquish must NOT be called for a cookie unless all
the cookies for "child" indices, objects and pages have been relinquished
first.
Expand Down
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