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Diffstat (limited to 'Documentation/filesystems/journalling.rst')
| -rw-r--r-- | Documentation/filesystems/journalling.rst | 37 |
1 files changed, 33 insertions, 4 deletions
diff --git a/Documentation/filesystems/journalling.rst b/Documentation/filesystems/journalling.rst index 7e2be2faf653..863e93e623f7 100644 --- a/Documentation/filesystems/journalling.rst +++ b/Documentation/filesystems/journalling.rst @@ -111,9 +111,7 @@ a callback function when the transaction is finally committed to disk, so that you can do some of your own management. You ask the journalling layer for calling the callback by simply setting ``journal->j_commit_callback`` function pointer and that function is -called after each transaction commit. You can also use -``transaction->t_private_list`` for attaching entries to a transaction -that need processing when the transaction commits. +called after each transaction commit. JBD2 also provides a way to block all transaction updates via jbd2_journal_lock_updates() / @@ -132,6 +130,37 @@ The opportunities for abuse and DOS attacks with this should be obvious, if you allow unprivileged userspace to trigger codepaths containing these calls. +Fast commits +~~~~~~~~~~~~ + +JBD2 to also allows you to perform file-system specific delta commits known as +fast commits. In order to use fast commits, you will need to set following +callbacks that perform corresponding work: + +`journal->j_fc_cleanup_cb`: Cleanup function called after every full commit and +fast commit. + +`journal->j_fc_replay_cb`: Replay function called for replay of fast commit +blocks. + +File system is free to perform fast commits as and when it wants as long as it +gets permission from JBD2 to do so by calling the function +:c:func:`jbd2_fc_begin_commit()`. Once a fast commit is done, the client +file system should tell JBD2 about it by calling +:c:func:`jbd2_fc_end_commit()`. If the file system wants JBD2 to perform a full +commit immediately after stopping the fast commit it can do so by calling +:c:func:`jbd2_fc_end_commit_fallback()`. This is useful if fast commit operation +fails for some reason and the only way to guarantee consistency is for JBD2 to +perform the full traditional commit. + +JBD2 helper functions to manage fast commit buffers. File system can use +:c:func:`jbd2_fc_get_buf()` and :c:func:`jbd2_fc_wait_bufs()` to allocate +and wait on IO completion of fast commit buffers. + +Currently, only Ext4 implements fast commits. For details of its implementation +of fast commits, please refer to the top level comments in +fs/ext4/fast_commit.c. + Summary ~~~~~~~ @@ -168,7 +197,7 @@ Journal Level .. kernel-doc:: fs/jbd2/recovery.c :internal: -Transasction Level +Transaction Level ~~~~~~~~~~~~~~~~~~ .. kernel-doc:: fs/jbd2/transaction.c |