Merge tag 'xarray-5.1-rc1' of git://git.infradead.org/users/willy/linux-dax

Pull XArray updates from Matthew Wilcox:
 "This pull request changes the xa_alloc() API. I'm only aware of one
  subsystem that has started trying to use it, and we agree on the fixup
  as part of the merge.

  The xa_insert() error code also changed to match xa_alloc() (EEXIST to
  EBUSY), and I added xa_alloc_cyclic(). Beyond that, the usual
  bugfixes, optimisations and tweaking.

  I now have a git tree with all users of the radix tree and IDR
  converted over to the XArray that I'll be feeding to maintainers over
  the next few weeks"

* tag 'xarray-5.1-rc1' of git://git.infradead.org/users/willy/linux-dax:
  XArray: Fix xa_reserve for 2-byte aligned entries
  XArray: Fix xa_erase of 2-byte aligned entries
  XArray: Use xa_cmpxchg to implement xa_reserve
  XArray: Fix xa_release in allocating arrays
  XArray: Mark xa_insert and xa_reserve as must_check
  XArray: Add cyclic allocation
  XArray: Redesign xa_alloc API
  XArray: Add support for 1s-based allocation
  XArray: Change xa_insert to return -EBUSY
  XArray: Update xa_erase family descriptions
  XArray tests: RCU lock prohibits GFP_KERNEL

1 files changed, 10 insertions, 5 deletions

diff --git a/Documentation/core-api/xarray.rst b/Documentation/core-api/xarray.rst
index 5d54b27c6eba..ef6f9f98f595 100644
--- a/Documentation/core-api/xarray.rst
+++ b/Documentation/core-api/xarray.rst
@@ -85,7 +85,7 @@ which was at that index; if it returns the same entry which was passed as
 
 If you want to only store a new entry to an index if the current entry
 at that index is ``NULL``, you can use :c:func:`xa_insert` which
-returns ``-EEXIST`` if the entry is not empty.
+returns ``-EBUSY`` if the entry is not empty.
 
 You can enquire whether a mark is set on an entry by using
 :c:func:`xa_get_mark`.  If the entry is not ``NULL``, you can set a mark
@@ -131,17 +131,23 @@ If you use :c:func:`DEFINE_XARRAY_ALLOC` to define the XArray, or
 initialise it by passing ``XA_FLAGS_ALLOC`` to :c:func:`xa_init_flags`,
 the XArray changes to track whether entries are in use or not.
 
-You can call :c:func:`xa_alloc` to store the entry at any unused index
+You can call :c:func:`xa_alloc` to store the entry at an unused index
 in the XArray.  If you need to modify the array from interrupt context,
 you can use :c:func:`xa_alloc_bh` or :c:func:`xa_alloc_irq` to disable
 interrupts while allocating the ID.
 
-Using :c:func:`xa_store`, :c:func:`xa_cmpxchg` or :c:func:`xa_insert`
-will mark the entry as being allocated.  Unlike a normal XArray, storing
+Using :c:func:`xa_store`, :c:func:`xa_cmpxchg` or :c:func:`xa_insert` will
+also mark the entry as being allocated.  Unlike a normal XArray, storing
 ``NULL`` will mark the entry as being in use, like :c:func:`xa_reserve`.
 To free an entry, use :c:func:`xa_erase` (or :c:func:`xa_release` if
 you only want to free the entry if it's ``NULL``).
 
+By default, the lowest free entry is allocated starting from 0.  If you
+want to allocate entries starting at 1, it is more efficient to use
+:c:func:`DEFINE_XARRAY_ALLOC1` or ``XA_FLAGS_ALLOC1``.  If you want to
+allocate IDs up to a maximum, then wrap back around to the lowest free
+ID, you can use :c:func:`xa_alloc_cyclic`.
+
 You cannot use ``XA_MARK_0`` with an allocating XArray as this mark
 is used to track whether an entry is free or not.  The other marks are
 available for your use.
@@ -209,7 +215,6 @@ Assumes xa_lock held on entry:
  * :c:func:`__xa_erase`
  * :c:func:`__xa_cmpxchg`
  * :c:func:`__xa_alloc`
- * :c:func:`__xa_reserve`
  * :c:func:`__xa_set_mark`
  * :c:func:`__xa_clear_mark`