From 90f9f118b75cbafc9114b6f2e8a7f87de170eea0 Mon Sep 17 00:00:00 2001 From: Mauro Carvalho Chehab Date: Fri, 12 May 2017 06:50:22 -0300 Subject: docs-rst: convert filesystems book to ReST Use pandoc to convert documentation to ReST by calling Documentation/sphinx/tmplcvt script. Signed-off-by: Mauro Carvalho Chehab --- Documentation/DocBook/filesystems.tmpl | 381 --------------------------------- 1 file changed, 381 deletions(-) delete mode 100644 Documentation/DocBook/filesystems.tmpl (limited to 'Documentation/DocBook/filesystems.tmpl') diff --git a/Documentation/DocBook/filesystems.tmpl b/Documentation/DocBook/filesystems.tmpl deleted file mode 100644 index 6006b6358c86..000000000000 --- a/Documentation/DocBook/filesystems.tmpl +++ /dev/null @@ -1,381 +0,0 @@ - - - - - - Linux Filesystems API - - - - This documentation is free software; you can redistribute - it and/or modify it under the terms of the GNU General Public - License as published by the Free Software Foundation; either - version 2 of the License, or (at your option) any later - version. - - - - This program is distributed in the hope that it will be - useful, but WITHOUT ANY WARRANTY; without even the implied - warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. - See the GNU General Public License for more details. - - - - You should have received a copy of the GNU General Public - License along with this program; if not, write to the Free - Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, - MA 02111-1307 USA - - - - For more details see the file COPYING in the source - distribution of Linux. - - - - - - - - The Linux VFS - The Filesystem types -!Iinclude/linux/fs.h - - The Directory Cache -!Efs/dcache.c -!Iinclude/linux/dcache.h - - Inode Handling -!Efs/inode.c -!Efs/bad_inode.c - - Registration and Superblocks -!Efs/super.c - - File Locks -!Efs/locks.c -!Ifs/locks.c - - Other Functions -!Efs/mpage.c -!Efs/namei.c -!Efs/buffer.c -!Eblock/bio.c -!Efs/seq_file.c -!Efs/filesystems.c -!Efs/fs-writeback.c -!Efs/block_dev.c - - - - - The proc filesystem - - sysctl interface -!Ekernel/sysctl.c - - - proc filesystem interface -!Ifs/proc/base.c - - - - - Events based on file descriptors -!Efs/eventfd.c - - - - The Filesystem for Exporting Kernel Objects -!Efs/sysfs/file.c -!Efs/sysfs/symlink.c - - - - The debugfs filesystem - - debugfs interface -!Efs/debugfs/inode.c -!Efs/debugfs/file.c - - - - - - The Linux Journalling API - - - - Roger - Gammans - -
- rgammans@computer-surgery.co.uk -
- - - - - - - Stephen - Tweedie - -
- sct@redhat.com -
- - - - - - 2002 - Roger Gammans - - - - The Linux Journalling API - - - Overview - - Details - -The journalling layer is easy to use. You need to -first of all create a journal_t data structure. There are -two calls to do this dependent on how you decide to allocate the physical -media on which the journal resides. The jbd2_journal_init_inode() call -is for journals stored in filesystem inodes, or the jbd2_journal_init_dev() -call can be used for journal stored on a raw device (in a continuous range -of blocks). A journal_t is a typedef for a struct pointer, so when -you are finally finished make sure you call jbd2_journal_destroy() on it -to free up any used kernel memory. - - - -Once you have got your journal_t object you need to 'mount' or load the journal -file. The journalling layer expects the space for the journal was already -allocated and initialized properly by the userspace tools. When loading the -journal you must call jbd2_journal_load() to process journal contents. If the -client file system detects the journal contents does not need to be processed -(or even need not have valid contents), it may call jbd2_journal_wipe() to -clear the journal contents before calling jbd2_journal_load(). - - - -Note that jbd2_journal_wipe(..,0) calls jbd2_journal_skip_recovery() for you if -it detects any outstanding transactions in the journal and similarly -jbd2_journal_load() will call jbd2_journal_recover() if necessary. I would -advise reading ext4_load_journal() in fs/ext4/super.c for examples on this -stage. - - - -Now you can go ahead and start modifying the underlying -filesystem. Almost. - - - - -You still need to actually journal your filesystem changes, this -is done by wrapping them into transactions. Additionally you -also need to wrap the modification of each of the buffers -with calls to the journal layer, so it knows what the modifications -you are actually making are. To do this use jbd2_journal_start() which -returns a transaction handle. - - - -jbd2_journal_start() -and its counterpart jbd2_journal_stop(), which indicates the end of a -transaction are nestable calls, so you can reenter a transaction if necessary, -but remember you must call jbd2_journal_stop() the same number of times as -jbd2_journal_start() before the transaction is completed (or more accurately -leaves the update phase). Ext4/VFS makes use of this feature to simplify -handling of inode dirtying, quota support, etc. - - - -Inside each transaction you need to wrap the modifications to the -individual buffers (blocks). Before you start to modify a buffer you -need to call jbd2_journal_get_{create,write,undo}_access() as appropriate, -this allows the journalling layer to copy the unmodified data if it -needs to. After all the buffer may be part of a previously uncommitted -transaction. -At this point you are at last ready to modify a buffer, and once -you are have done so you need to call jbd2_journal_dirty_{meta,}data(). -Or if you've asked for access to a buffer you now know is now longer -required to be pushed back on the device you can call jbd2_journal_forget() -in much the same way as you might have used bforget() in the past. - - - -A jbd2_journal_flush() may be called at any time to commit and checkpoint -all your transactions. - - - -Then at umount time , in your put_super() you can then call jbd2_journal_destroy() -to clean up your in-core journal object. - - - -Unfortunately there a couple of ways the journal layer can cause a deadlock. -The first thing to note is that each task can only have -a single outstanding transaction at any one time, remember nothing -commits until the outermost jbd2_journal_stop(). This means -you must complete the transaction at the end of each file/inode/address -etc. operation you perform, so that the journalling system isn't re-entered -on another journal. Since transactions can't be nested/batched -across differing journals, and another filesystem other than -yours (say ext4) may be modified in a later syscall. - - - -The second case to bear in mind is that jbd2_journal_start() can -block if there isn't enough space in the journal for your transaction -(based on the passed nblocks param) - when it blocks it merely(!) needs to -wait for transactions to complete and be committed from other tasks, -so essentially we are waiting for jbd2_journal_stop(). So to avoid -deadlocks you must treat jbd2_journal_start/stop() as if they -were semaphores and include them in your semaphore ordering rules to prevent -deadlocks. Note that jbd2_journal_extend() has similar blocking behaviour to -jbd2_journal_start() so you can deadlock here just as easily as on -jbd2_journal_start(). - - - -Try to reserve the right number of blocks the first time. ;-). This will -be the maximum number of blocks you are going to touch in this transaction. -I advise having a look at at least ext4_jbd.h to see the basis on which -ext4 uses to make these decisions. - - - -Another wriggle to watch out for is your on-disk block allocation strategy. -Why? Because, if you do a delete, you need to ensure you haven't reused any -of the freed blocks until the transaction freeing these blocks commits. If you -reused these blocks and crash happens, there is no way to restore the contents -of the reallocated blocks at the end of the last fully committed transaction. - -One simple way of doing this is to mark blocks as free in internal in-memory -block allocation structures only after the transaction freeing them commits. -Ext4 uses journal commit callback for this purpose. - - - -With journal commit callbacks you can ask the journalling layer to call 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. - - - -JBD2 also provides a way to block all transaction updates via -jbd2_journal_{un,}lock_updates(). Ext4 uses this when it wants a window with a -clean and stable fs for a moment. E.g. - - - - - jbd2_journal_lock_updates() //stop new stuff happening.. - jbd2_journal_flush() // checkpoint everything. - ..do stuff on stable fs - jbd2_journal_unlock_updates() // carry on with filesystem use. - - - -The opportunities for abuse and DOS attacks with this should be obvious, -if you allow unprivileged userspace to trigger codepaths containing these -calls. - - - - - - Summary - -Using the journal is a matter of wrapping the different context changes, -being each mount, each modification (transaction) and each changed buffer -to tell the journalling layer about them. - - - - - - - - Data Types - - The journalling layer uses typedefs to 'hide' the concrete definitions - of the structures used. As a client of the JBD2 layer you can - just rely on the using the pointer as a magic cookie of some sort. - - Obviously the hiding is not enforced as this is 'C'. - - Structures -!Iinclude/linux/jbd2.h - - - - - Functions - - The functions here are split into two groups those that - affect a journal as a whole, and those which are used to - manage transactions - - Journal Level -!Efs/jbd2/journal.c -!Ifs/jbd2/recovery.c - - Transasction Level -!Efs/jbd2/transaction.c - - - - See also - - - - Journaling the Linux ext2fs Filesystem, LinuxExpo 98, Stephen Tweedie - - - - - - - Ext3 Journalling FileSystem, OLS 2000, Dr. Stephen Tweedie - - - - - - - - - splice API - - splice is a method for moving blocks of data around inside the - kernel, without continually transferring them between the kernel - and user space. - -!Ffs/splice.c - - - - pipes API - - Pipe interfaces are all for in-kernel (builtin image) use. - They are not exported for use by modules. - -!Iinclude/linux/pipe_fs_i.h -!Ffs/pipe.c - - - -- cgit v1.2.3