diff options
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/DocBook/filesystems.tmpl | 178 | ||||
| -rw-r--r-- | Documentation/filesystems/ext2.txt | 4 | ||||
| -rw-r--r-- | Documentation/filesystems/ext3.txt | 209 | ||||
| -rw-r--r-- | Documentation/filesystems/vfs.txt | 2 |
4 files changed, 73 insertions, 320 deletions
diff --git a/Documentation/DocBook/filesystems.tmpl b/Documentation/DocBook/filesystems.tmpl index bcdfdb9a9277..6006b6358c86 100644 --- a/Documentation/DocBook/filesystems.tmpl +++ b/Documentation/DocBook/filesystems.tmpl @@ -146,36 +146,30 @@ 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 journal_init_inode() call -is for journals stored in filesystem inodes, or the journal_init_dev() -call can be use for journal stored on a raw device (in a continuous range +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 journal_destroy() on it +you are finally finished make sure you call jbd2_journal_destroy() on it to free up any used kernel memory. </para> <para> Once you have got your journal_t object you need to 'mount' or load the journal -file, unless of course you haven't initialised it yet - in which case you -need to call journal_create(). +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(). </para> <para> -Most of the time however your journal file will already have been created, but -before you load it you must call journal_wipe() to empty the journal file. -Hang on, you say , what if the filesystem wasn't cleanly umount()'d . Well, it is the -job of the client file system to detect this and skip the call to journal_wipe(). -</para> - -<para> -In either case the next call should be to journal_load() which prepares the -journal file for use. Note that journal_wipe(..,0) calls journal_skip_recovery() -for you if it detects any outstanding transactions in the journal and similarly -journal_load() will call journal_recover() if necessary. -I would advise reading fs/ext3/super.c for examples on this stage. -[RGG: Why is the journal_wipe() call necessary - doesn't this needlessly -complicate the API. Or isn't a good idea for the journal layer to hide -dirty mounts from the client fs] +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. </para> <para> @@ -189,41 +183,41 @@ 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 journal_start() which +you are actually making are. To do this use jbd2_journal_start() which returns a transaction handle. </para> <para> -journal_start() -and its counterpart 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 journal_stop() the same number of times as -journal_start() before the transaction is completed (or more accurately -leaves the update phase). Ext3/VFS makes use of this feature to simplify -quota support. +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. </para> <para> 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 journal_get_{create,write,undo}_access() as appropriate, +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 journal_dirty_{meta,}data(). +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 journal_forget() +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. </para> <para> -A journal_flush() may be called at any time to commit and checkpoint +A jbd2_journal_flush() may be called at any time to commit and checkpoint all your transactions. </para> <para> -Then at umount time , in your put_super() you can then call journal_destroy() +Then at umount time , in your put_super() you can then call jbd2_journal_destroy() to clean up your in-core journal object. </para> @@ -231,53 +225,68 @@ 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 journal_stop(). This means +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 ext3) may be modified in a later syscall. +yours (say ext4) may be modified in a later syscall. </para> <para> -The second case to bear in mind is that journal_start() can +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 journal_stop(). So to avoid -deadlocks you must treat journal_start/stop() as if they +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 journal_extend() has similar blocking behaviour to -journal_start() so you can deadlock here just as easily as on journal_start(). +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(). </para> <para> 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 ext3_jbd.h to see the basis on which -ext3 uses to make these decisions. +I advise having a look at at least ext4_jbd.h to see the basis on which +ext4 uses to make these decisions. </para> <para> Another wriggle to watch out for is your on-disk block allocation strategy. -why? Because, if you undo a delete, you need to ensure you haven't reused any -of the freed blocks in a later transaction. One simple way of doing this -is make sure any blocks you allocate only have checkpointed transactions -listed against them. Ext3 does this in ext3_test_allocatable(). +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. +</para> + +<para> +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. </para> <para> -Lock is also providing through journal_{un,}lock_updates(), -ext3 uses this when it wants a window with a clean and stable fs for a moment. -eg. +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. </para> <programlisting> - journal_lock_updates() //stop new stuff happening.. - journal_flush() // checkpoint everything. + jbd2_journal_lock_updates() //stop new stuff happening.. + jbd2_journal_flush() // checkpoint everything. ..do stuff on stable fs - journal_unlock_updates() // carry on with filesystem use. + jbd2_journal_unlock_updates() // carry on with filesystem use. </programlisting> <para> @@ -286,29 +295,6 @@ if you allow unprivileged userspace to trigger codepaths containing these calls. </para> -<para> -A new feature of jbd since 2.5.25 is commit callbacks with the new -journal_callback_set() function you can now ask the journalling layer -to call you back when the transaction is finally committed to disk, so that -you can do some of your own management. The key to this is the journal_callback -struct, this maintains the internal callback information but you can -extend it like this:- -</para> -<programlisting> - struct myfs_callback_s { - //Data structure element required by jbd.. - struct journal_callback for_jbd; - // Stuff for myfs allocated together. - myfs_inode* i_commited; - - } -</programlisting> - -<para> -this would be useful if you needed to know when data was committed to a -particular inode. -</para> - </sect2> <sect2 id="jbd_summary"> @@ -319,36 +305,6 @@ being each mount, each modification (transaction) and each changed buffer to tell the journalling layer about them. </para> -<para> -Here is a some pseudo code to give you an idea of how it works, as -an example. -</para> - -<programlisting> - journal_t* my_jnrl = journal_create(); - journal_init_{dev,inode}(jnrl,...) - if (clean) journal_wipe(); - journal_load(); - - foreach(transaction) { /*transactions must be - completed before - a syscall returns to - userspace*/ - - handle_t * xct=journal_start(my_jnrl); - foreach(bh) { - journal_get_{create,write,undo}_access(xact,bh); - if ( myfs_modify(bh) ) { /* returns true - if makes changes */ - journal_dirty_{meta,}data(xact,bh); - } else { - journal_forget(bh); - } - } - journal_stop(xct); - } - journal_destroy(my_jrnl); -</programlisting> </sect2> </sect1> @@ -357,13 +313,13 @@ an example. <title>Data Types</title> <para> The journalling layer uses typedefs to 'hide' the concrete definitions - of the structures used. As a client of the JBD layer you can + 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'. </para> <sect2 id="structures"><title>Structures</title> -!Iinclude/linux/jbd.h +!Iinclude/linux/jbd2.h </sect2> </sect1> @@ -375,11 +331,11 @@ an example. manage transactions </para> <sect2 id="journal_level"><title>Journal Level</title> -!Efs/jbd/journal.c -!Ifs/jbd/recovery.c +!Efs/jbd2/journal.c +!Ifs/jbd2/recovery.c </sect2> <sect2 id="transaction_level"><title>Transasction Level</title> -!Efs/jbd/transaction.c +!Efs/jbd2/transaction.c </sect2> </sect1> <sect1 id="see_also"> diff --git a/Documentation/filesystems/ext2.txt b/Documentation/filesystems/ext2.txt index b9714569e472..55755395d3dc 100644 --- a/Documentation/filesystems/ext2.txt +++ b/Documentation/filesystems/ext2.txt @@ -360,8 +360,8 @@ and are copied into the filesystem. If a transaction is incomplete at the time of the crash, then there is no guarantee of consistency for the blocks in that transaction so they are discarded (which means any filesystem changes they represent are also lost). -Check Documentation/filesystems/ext3.txt if you want to read more about -ext3 and journaling. +Check Documentation/filesystems/ext4.txt if you want to read more about +ext4 and journaling. References ========== diff --git a/Documentation/filesystems/ext3.txt b/Documentation/filesystems/ext3.txt index 7ed0d17d6721..58758fbef9e0 100644 --- a/Documentation/filesystems/ext3.txt +++ b/Documentation/filesystems/ext3.txt @@ -6,210 +6,7 @@ Ext3 was originally released in September 1999. Written by Stephen Tweedie for the 2.2 branch, and ported to 2.4 kernels by Peter Braam, Andreas Dilger, Andrew Morton, Alexander Viro, Ted Ts'o and Stephen Tweedie. -Ext3 is the ext2 filesystem enhanced with journalling capabilities. +Ext3 is the ext2 filesystem enhanced with journalling capabilities. The +filesystem is a subset of ext4 filesystem so use ext4 driver for accessing +ext3 filesystems. -Options -======= - -When mounting an ext3 filesystem, the following option are accepted: -(*) == default - -ro Mount filesystem read only. Note that ext3 will replay - the journal (and thus write to the partition) even when - mounted "read only". Mount options "ro,noload" can be - used to prevent writes to the filesystem. - -journal=update Update the ext3 file system's journal to the current - format. - -journal=inum When a journal already exists, this option is ignored. - Otherwise, it specifies the number of the inode which - will represent the ext3 file system's journal file. - -journal_path=path -journal_dev=devnum When the external journal device's major/minor numbers - have changed, these options allow the user to specify - the new journal location. The journal device is - identified through either its new major/minor numbers - encoded in devnum, or via a path to the device. - -norecovery Don't load the journal on mounting. Note that this forces -noload mount of inconsistent filesystem, which can lead to - various problems. - -data=journal All data are committed into the journal prior to being - written into the main file system. - -data=ordered (*) All data are forced directly out to the main file - system prior to its metadata being committed to the - journal. - -data=writeback Data ordering is not preserved, data may be written - into the main file system after its metadata has been - committed to the journal. - -commit=nrsec (*) Ext3 can be told to sync all its data and metadata - every 'nrsec' seconds. The default value is 5 seconds. - This means that if you lose your power, you will lose - as much as the latest 5 seconds of work (your - filesystem will not be damaged though, thanks to the - journaling). This default value (or any low value) - will hurt performance, but it's good for data-safety. - Setting it to 0 will have the same effect as leaving - it at the default (5 seconds). - Setting it to very large values will improve - performance. - -barrier=<0|1(*)> This enables/disables the use of write barriers in -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 - of journal commits, making volatile disk write caches - 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 ext3 mount options. - -user_xattr Enables Extended User Attributes. Additionally, you - need to have extended attribute support enabled in the - kernel configuration (CONFIG_EXT3_FS_XATTR). See the - attr(5) manual page and http://acl.bestbits.at/ to - learn more about extended attributes. - -nouser_xattr Disables Extended User Attributes. - -acl Enables POSIX Access Control Lists support. - Additionally, you need to have ACL support enabled in - the kernel configuration (CONFIG_EXT3_FS_POSIX_ACL). - See the acl(5) manual page and http://acl.bestbits.at/ - for more information. - -noacl This option disables POSIX Access Control List - support. - -reservation - -noreservation - -bsddf (*) Make 'df' act like BSD. -minixdf Make 'df' act like Minix. - -check=none Don't do extra checking of bitmaps on mount. -nocheck - -debug Extra debugging information is sent to syslog. - -errors=remount-ro Remount the filesystem read-only on an error. -errors=continue Keep going on a filesystem error. -errors=panic Panic and halt the machine if an error occurs. - (These mount options override the errors behavior - specified in the superblock, which can be - configured using tune2fs.) - -data_err=ignore(*) Just print an error message if an error occurs - in a file data buffer in ordered mode. -data_err=abort Abort the journal if an error occurs in a file - data buffer in ordered mode. - -grpid Give objects the same group ID as their creator. -bsdgroups - -nogrpid (*) New objects have the group ID of their creator. -sysvgroups - -resgid=n The group ID which may use the reserved blocks. - -resuid=n The user ID which may use the reserved blocks. - -sb=n Use alternate superblock at this location. - -quota These options are ignored by the filesystem. They -noquota are used only by quota tools to recognize volumes -grpquota where quota should be turned on. See documentation -usrquota in the quota-tools package for more details - (http://sourceforge.net/projects/linuxquota). - -jqfmt=<quota type> These options tell filesystem details about quota -usrjquota=<file> so that quota information can be properly updated -grpjquota=<file> during journal replay. They replace the above - quota options. See documentation in the quota-tools - package for more details - (http://sourceforge.net/projects/linuxquota). - -Specification -============= -Ext3 shares all disk implementation with the ext2 filesystem, and adds -transactions capabilities to ext2. Journaling is done by the Journaling Block -Device layer. - -Journaling Block Device layer ------------------------------ -The Journaling Block Device layer (JBD) isn't ext3 specific. It was designed -to add journaling capabilities to a block device. The ext3 filesystem code -will inform the JBD of modifications it is performing (called a transaction). -The journal supports the transactions start and stop, and in case of a crash, -the journal can replay the transactions to quickly put the partition back into -a consistent state. - -Handles represent a single atomic update to a filesystem. JBD can handle an -external journal on a block device. - -Data Mode ---------- -There are 3 different data modes: - -* writeback mode -In data=writeback mode, ext3 does not journal data at all. This mode provides -a similar level of journaling as that of XFS, JFS, and ReiserFS in its default -mode - metadata journaling. A crash+recovery can cause incorrect data to -appear in files which were written shortly before the crash. This mode will -typically provide the best ext3 performance. - -* ordered mode -In data=ordered mode, ext3 only officially journals metadata, but it logically -groups metadata and data blocks into a single unit called a transaction. When -it's time to write the new metadata out to disk, the associated data blocks -are written first. In general, this mode performs slightly slower than -writeback but significantly faster than journal mode. - -* journal mode -data=journal mode provides full data and metadata journaling. All new data is -written to the journal first, and then to its final location. -In the event of a crash, the journal can be replayed, bringing both data and -metadata into a consistent state. This mode is the slowest except when data -needs to be read from and written to disk at the same time where it -outperforms all other modes. - -Compatibility -------------- - -Ext2 partitions can be easily convert to ext3, with `tune2fs -j <dev>`. -Ext3 is fully compatible with Ext2. Ext3 partitions can easily be mounted as -Ext2. - - -External Tools -============== -See manual pages to learn more. - -tune2fs: create a ext3 journal on a ext2 partition with the -j flag. -mke2fs: create a ext3 partition with the -j flag. -debugfs: ext2 and ext3 file system debugger. -ext2online: online (mounted) ext2 and ext3 filesystem resizer - - -References -========== - -kernel source: <file:fs/ext3/> - <file:fs/jbd/> - -programs: http://e2fsprogs.sourceforge.net/ - http://ext2resize.sourceforge.net - -useful links: http://www.ibm.com/developerworks/library/l-fs7/index.html - http://www.ibm.com/developerworks/library/l-fs8/index.html diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt index 5eb8456fc41e..8c6f07ad373a 100644 --- a/Documentation/filesystems/vfs.txt +++ b/Documentation/filesystems/vfs.txt @@ -769,7 +769,7 @@ struct address_space_operations { to stall to allow flushers a chance to complete some IO. Ordinarily it can use PageDirty and PageWriteback but some filesystems have more complex state (unstable pages in NFS prevent reclaim) or - do not set those flags due to locking problems (jbd). This callback + do not set those flags due to locking problems. This callback allows a filesystem to indicate to the VM if a page should be treated as dirty or writeback for the purposes of stalling. |