Merge git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6

[pandora-kernel.git] / Documentation / filesystems / ext4.txt

diff --git a/Documentation/filesystems/ext4.txt b/Documentation/filesystems/ext4.txt
index cec829b..97882df 100644 (file)
--- a/Documentation/filesystems/ext4.txt
+++ b/Documentation/filesystems/ext4.txt
@@ -85,7 +85,7 @@ Note: More extensive information for getting started with ext4 can be
 * extent format more robust in face of on-disk corruption due to magics,
 * internal redundancy in tree
 * improved file allocation (multi-block alloc)
-* fix 32000 subdirectory limit
+* lift 32000 subdirectory limit imposed by i_links_count[1]
 * nsec timestamps for mtime, atime, ctime, create time
 * inode version field on disk (NFSv4, Lustre)
 * reduced e2fsck time via uninit_bg feature
@@ -100,6 +100,9 @@ Note: More extensive information for getting started with ext4 can be
 * efficent new ordered mode in JBD2 and ext4(avoid using buffer head to force
   the ordering)
 
+[1] Filesystems with a block size of 1k may see a limit imposed by the
+directory hash tree having a maximum depth of two.
+
 2.2 Candidate features for future inclusion
 
 * Online defrag (patches available but not well tested)
@@ -180,8 +183,8 @@ commit=nrsec        (*)     Ext4 can be told to sync all its data and metadata
                        performance.
 
 barrier=<0|1(*)>       This enables/disables the use of write barriers in
-                       the jbd code.  barrier=0 disables, barrier=1 enables.
-                       This also requires an IO stack which can support
+barrier(*)             the jbd code.  barrier=0 disables, barrier=1 enables.
+nobarrier              This also requires an IO stack which can support
                        barriers, and if jbd gets an error on a barrier
                        write, it will disable again with a warning.
                        Write barriers enforce proper on-disk ordering
@@ -189,6 +192,9 @@ barrier=<0|1(*)>    This enables/disables the use of write barriers in
                        safe to use, at some performance penalty.  If
                        your disks are battery-backed in one way or another,
                        disabling barriers may safely improve performance.
+                       The mount options "barrier" and "nobarrier" can
+                       also be used to enable or disable barriers, for
+                       consistency with other ext4 mount options.
 
 inode_readahead=n      This tuning parameter controls the maximum
                        number of inode table blocks that ext4's inode
@@ -310,6 +316,24 @@ journal_ioprio=prio        The I/O priority (from 0 to 7, where 0 is the
                        a slightly higher priority than the default I/O
                        priority.
 
+auto_da_alloc(*)       Many broken applications don't use fsync() when 
+noauto_da_alloc                replacing existing files via patterns such as
+                       fd = open("foo.new")/write(fd,..)/close(fd)/
+                       rename("foo.new", "foo"), or worse yet,
+                       fd = open("foo", O_TRUNC)/write(fd,..)/close(fd).
+                       If auto_da_alloc is enabled, ext4 will detect
+                       the replace-via-rename and replace-via-truncate
+                       patterns and force that any delayed allocation
+                       blocks are allocated such that at the next
+                       journal commit, in the default data=ordered
+                       mode, the data blocks of the new file are forced
+                       to disk before the rename() operation is
+                       commited.  This provides roughly the same level
+                       of guarantees as ext3, and avoids the
+                       "zero-length" problem that can happen when a
+                       system crashes before the delayed allocation
+                       blocks are forced to disk.
+
 Data Mode
 =========
 There are 3 different data modes: