Message-Id: <20191120185412.302-2-daniel.m.jordan@oracle.com>
Date:   Wed, 20 Nov 2019 13:54:09 -0500
From:   Daniel Jordan <daniel.m.jordan@...cle.com>
To:     Herbert Xu <herbert@...dor.apana.org.au>,
        Steffen Klassert <steffen.klassert@...unet.com>
Cc:     Eric Biggers <ebiggers@...nel.org>, linux-crypto@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Daniel Jordan <daniel.m.jordan@...cle.com>,
        Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org
Subject: [PATCH 1/4] padata: update documentation

Remove references to unused functions and update to reflect the new
struct padata_shell.

Fixes: 815613da6a67 ("kernel/padata.c: removed unused code")
Signed-off-by: Daniel Jordan <daniel.m.jordan@...cle.com>
Cc: Eric Biggers <ebiggers@...nel.org>
Cc: Herbert Xu <herbert@...dor.apana.org.au>
Cc: Jonathan Corbet <corbet@....net>
Cc: Steffen Klassert <steffen.klassert@...unet.com>
Cc: linux-crypto@...r.kernel.org
Cc: linux-doc@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
---
 Documentation/padata.txt | 50 +++++++++++++++++++++-------------------
 1 file changed, 26 insertions(+), 24 deletions(-)

diff --git a/Documentation/padata.txt b/Documentation/padata.txt
index b37ba1eaace3..a03afb1588f9 100644
--- a/Documentation/padata.txt
+++ b/Documentation/padata.txt
@@ -2,7 +2,7 @@
 The padata parallel execution mechanism
 =======================================
 
-:Last updated: for 2.6.36
+:Last updated: for 5.4
 
 Padata is a mechanism by which the kernel can farm work out to be done in
 parallel on multiple CPUs while retaining the ordering of tasks.  It was
@@ -53,27 +53,26 @@ padata cpumask contains no active CPU (flag not set).
 padata_stop clears the flag and blocks until the padata instance
 is unused.
 
-The list of CPUs to be used can be adjusted with these functions::
+Finally, complete padata initialization by allocating a padata_shell object::
+
+   struct padata_shell *padata_alloc_shell(struct padata_instance *pinst);
+
+A padata_shell is used to submit a job to padata and allows a series of such
+jobs to be serialized independently.  A padata_instance may have one or more
+padata_shell objects associated with it, each allowing a separate series of
+jobs.
+
+The list of CPUs to be used can be adjusted with this function::
 
-    int padata_set_cpumasks(struct padata_instance *pinst,
-			    cpumask_var_t pcpumask,
-			    cpumask_var_t cbcpumask);
     int padata_set_cpumask(struct padata_instance *pinst, int cpumask_type,
 			   cpumask_var_t cpumask);
-    int padata_add_cpu(struct padata_instance *pinst, int cpu, int mask);
-    int padata_remove_cpu(struct padata_instance *pinst, int cpu, int mask);
 
 Changing the CPU masks are expensive operations, though, so it should not be
 done with great frequency.
 
-It's possible to change both cpumasks of a padata instance with
-padata_set_cpumasks by specifying the cpumasks for parallel execution (pcpumask)
-and for the serial callback function (cbcpumask). padata_set_cpumask is used to
-change just one of the cpumasks. Here cpumask_type is one of PADATA_CPU_SERIAL,
-PADATA_CPU_PARALLEL and cpumask specifies the new cpumask to use.
-To simply add or remove one CPU from a certain cpumask the functions
-padata_add_cpu/padata_remove_cpu are used. cpu specifies the CPU to add or
-remove and mask is one of PADATA_CPU_SERIAL, PADATA_CPU_PARALLEL.
+padata_set_cpumask is used to change just one of the cpumasks. Here cpumask_type
+is one of PADATA_CPU_SERIAL or PADATA_CPU_PARALLEL, and cpumask specifies the
+new cpumask to use.
 
 If a user is interested in padata cpumask changes, he can register to
 the padata cpumask change notifier::
@@ -117,12 +116,13 @@ momentarily.
 
 The submission of work is done with::
 
-    int padata_do_parallel(struct padata_instance *pinst,
-		           struct padata_priv *padata, int cb_cpu);
+    int padata_do_parallel(struct padata_shell *ps,
+		           struct padata_priv *padata, int *cb_cpu);
 
-The pinst and padata structures must be set up as described above; cb_cpu
-specifies which CPU will be used for the final callback when the work is
-done; it must be in the current instance's CPU mask.  The return value from
+The ps and padata structures must be set up as described above; cb_cpu
+points to the preferred CPU to be used for the final callback when the work is
+done; it must be in the current instance's CPU mask (if not the cb_cpu pointer
+is updated to point to the CPU actually chosen).  The return value from
 padata_do_parallel() is zero on success, indicating that the work is in
 progress. -EBUSY means that somebody, somewhere else is messing with the
 instance's CPU mask, while -EINVAL is a complaint about cb_cpu not being
@@ -154,10 +154,12 @@ Note that this call may be deferred for a while since the padata code takes
 pains to ensure that tasks are completed in the order in which they were
 submitted.
 
-The one remaining function in the padata API should be called to clean up
-when a padata instance is no longer needed::
+Cleaning up a padata instance predictably involves calling the three free
+functions that correspond to the allocation in reverse:
 
+    void padata_free_shell(struct padata_shell *ps);
+    void padata_stop(struct padata_instance *pinst);
     void padata_free(struct padata_instance *pinst);
 
-This function will busy-wait while any remaining tasks are completed, so it
-might be best not to call it while there is work outstanding.
+It is the user's responsibility to ensure all outstanding jobs are complete
+before any of the above are called.
-- 
2.23.0

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