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-rw-r--r--Documentation/filesystems/porting45
1 files changed, 45 insertions, 0 deletions
diff --git a/Documentation/filesystems/porting b/Documentation/filesystems/porting
index a7e9746ee7e..b12c8953868 100644
--- a/Documentation/filesystems/porting
+++ b/Documentation/filesystems/porting
@@ -273,3 +273,48 @@ it's safe to remove it. If you don't need it, remove it.
deliberate; as soon as struct block_device * is propagated in a reasonable
way by that code fixing will become trivial; until then nothing can be
done.
+
+[mandatory]
+
+ block truncatation on error exit from ->write_begin, and ->direct_IO
+moved from generic methods (block_write_begin, cont_write_begin,
+nobh_write_begin, blockdev_direct_IO*) to callers. Take a look at
+ext2_write_failed and callers for an example.
+
+[mandatory]
+
+ ->truncate is going away. The whole truncate sequence needs to be
+implemented in ->setattr, which is now mandatory for filesystems
+implementing on-disk size changes. Start with a copy of the old inode_setattr
+and vmtruncate, and the reorder the vmtruncate + foofs_vmtruncate sequence to
+be in order of zeroing blocks using block_truncate_page or similar helpers,
+size update and on finally on-disk truncation which should not fail.
+inode_change_ok now includes the size checks for ATTR_SIZE and must be called
+in the beginning of ->setattr unconditionally.
+
+[mandatory]
+
+ ->clear_inode() and ->delete_inode() are gone; ->evict_inode() should
+be used instead. It gets called whenever the inode is evicted, whether it has
+remaining links or not. Caller does *not* evict the pagecache or inode-associated
+metadata buffers; getting rid of those is responsibility of method, as it had
+been for ->delete_inode().
+ ->drop_inode() returns int now; it's called on final iput() with inode_lock
+held and it returns true if filesystems wants the inode to be dropped. As before,
+generic_drop_inode() is still the default and it's been updated appropriately.
+generic_delete_inode() is also alive and it consists simply of return 1. Note that
+all actual eviction work is done by caller after ->drop_inode() returns.
+ clear_inode() is gone; use end_writeback() instead. As before, it must
+be called exactly once on each call of ->evict_inode() (as it used to be for
+each call of ->delete_inode()). Unlike before, if you are using inode-associated
+metadata buffers (i.e. mark_buffer_dirty_inode()), it's your responsibility to
+call invalidate_inode_buffers() before end_writeback().
+ No async writeback (and thus no calls of ->write_inode()) will happen
+after end_writeback() returns, so actions that should not overlap with ->write_inode()
+(e.g. freeing on-disk inode if i_nlink is 0) ought to be done after that call.
+
+ NOTE: checking i_nlink in the beginning of ->write_inode() and bailing out
+if it's zero is not *and* *never* *had* *been* enough. Final unlink() and iput()
+may happen while the inode is in the middle of ->write_inode(); e.g. if you blindly
+free the on-disk inode, you may end up doing that while ->write_inode() is writing
+to it.