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/filesystems/conf.py | 10 ++ Documentation/filesystems/index.rst | 314 ++++++++++++++++++++++++++++++++++++ 2 files changed, 324 insertions(+) create mode 100644 Documentation/filesystems/conf.py create mode 100644 Documentation/filesystems/index.rst (limited to 'Documentation/filesystems') diff --git a/Documentation/filesystems/conf.py b/Documentation/filesystems/conf.py new file mode 100644 index 000000000000..ea44172af5c4 --- /dev/null +++ b/Documentation/filesystems/conf.py @@ -0,0 +1,10 @@ +# -*- coding: utf-8; mode: python -*- + +project = "Linux Filesystems API" + +tags.add("subproject") + +latex_documents = [ + ('index', 'filesystems.tex', project, + 'The kernel development community', 'manual'), +] diff --git a/Documentation/filesystems/index.rst b/Documentation/filesystems/index.rst new file mode 100644 index 000000000000..3bc82e9d22f0 --- /dev/null +++ b/Documentation/filesystems/index.rst @@ -0,0 +1,314 @@ +===================== +Linux Filesystems API +===================== + +The Linux VFS +============= + +The Filesystem types +-------------------- + +.. kernel-doc:: include/linux/fs.h + :internal: + +The Directory Cache +------------------- + +.. kernel-doc:: fs/dcache.c + :export: + +.. kernel-doc:: include/linux/dcache.h + :internal: + +Inode Handling +-------------- + +.. kernel-doc:: fs/inode.c + :export: + +.. kernel-doc:: fs/bad_inode.c + :export: + +Registration and Superblocks +---------------------------- + +.. kernel-doc:: fs/super.c + :export: + +File Locks +---------- + +.. kernel-doc:: fs/locks.c + :export: + +.. kernel-doc:: fs/locks.c + :internal: + +Other Functions +--------------- + +.. kernel-doc:: fs/mpage.c + :export: + +.. kernel-doc:: fs/namei.c + :export: + +.. kernel-doc:: fs/buffer.c + :export: + +.. kernel-doc:: block/bio.c + :export: + +.. kernel-doc:: fs/seq_file.c + :export: + +.. kernel-doc:: fs/filesystems.c + :export: + +.. kernel-doc:: fs/fs-writeback.c + :export: + +.. kernel-doc:: fs/block_dev.c + :export: + +The proc filesystem +=================== + +sysctl interface +---------------- + +.. kernel-doc:: kernel/sysctl.c + :export: + +proc filesystem interface +------------------------- + +.. kernel-doc:: fs/proc/base.c + :internal: + +Events based on file descriptors +================================ + +.. kernel-doc:: fs/eventfd.c + :export: + +The Filesystem for Exporting Kernel Objects +=========================================== + +.. kernel-doc:: fs/sysfs/file.c + :export: + +.. kernel-doc:: fs/sysfs/symlink.c + :export: + +The debugfs filesystem +====================== + +debugfs interface +----------------- + +.. kernel-doc:: fs/debugfs/inode.c + :export: + +.. kernel-doc:: fs/debugfs/file.c + :export: + +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 +~~~~~~~~~~ + +.. kernel-doc:: include/linux/jbd2.h + :internal: + +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 +~~~~~~~~~~~~~ + +.. kernel-doc:: fs/jbd2/journal.c + :export: + +.. kernel-doc:: fs/jbd2/recovery.c + :internal: + +Transasction Level +~~~~~~~~~~~~~~~~~~ + +.. kernel-doc:: fs/jbd2/transaction.c + :export: + +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. + +.. kernel-doc:: fs/splice.c + +pipes API +========= + +Pipe interfaces are all for in-kernel (builtin image) use. They are not +exported for use by modules. + +.. kernel-doc:: include/linux/pipe_fs_i.h + :internal: + +.. kernel-doc:: fs/pipe.c -- cgit From 7a2208f636cc05c06593832bae9f599c73437322 Mon Sep 17 00:00:00 2001 From: Mauro Carvalho Chehab Date: Fri, 12 May 2017 07:15:19 -0300 Subject: docs-rst: filesystems: use c domain references where needed Instead of just mention the function names, use cross-references to the kernel-doc tags where pertinent. While not all function documentation is included here, I double-checked that all functions mentioned there still exists. Signed-off-by: Mauro Carvalho Chehab --- Documentation/filesystems/index.rst | 76 +++++++++++++++++++------------------ 1 file changed, 40 insertions(+), 36 deletions(-) (limited to 'Documentation/filesystems') diff --git a/Documentation/filesystems/index.rst b/Documentation/filesystems/index.rst index 3bc82e9d22f0..148becd91cba 100644 --- a/Documentation/filesystems/index.rst +++ b/Documentation/filesystems/index.rst @@ -125,27 +125,27 @@ 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 +resides. The :c:func:`jbd2_journal_init_inode` call is for journals stored in +filesystem inodes, or the :c:func:`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 +finished make sure you call :c:func:`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 +When loading the journal you must call :c:func:`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(). +may call :c:func:`jbd2_journal_wipe` to clear the journal contents before +calling :c:func:`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. +:c:func:`jbd2_journal_skip_recovery` for you if it detects any outstanding +transactions in the journal and similarly :c:func:`jbd2_journal_load` will +call :c:func:`jbd2_journal_recover` if necessary. I would advise reading +:c:func:`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. @@ -154,54 +154,57 @@ 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. +this use :c:func:`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 +:c:func:`jbd2_journal_start` and its counterpart :c:func:`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. +:c:func:`jbd2_journal_stop` the same number of times as +:c:func:`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 +need to call :c:func:`jbd2_journal_get_create_access()` / +:c:func:`jbd2_journal_get_write_access()` / +:c:func:`jbd2_journal_get_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 +:c:func:`jbd2_journal_dirty_metadata`. 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. +device you can call :c:func:`jbd2_journal_forget` in much the same way as you +might have used :c:func:`bforget` in the past. -A jbd2_journal_flush() may be called at any time to commit and +A :c:func:`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. +Then at umount time , in your :c:func:`put_super` you can then call +:c:func:`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 +until the outermost :c:func:`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 +The second case to bear in mind is that :c:func:`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(). +essentially we are waiting for :c:func:`jbd2_journal_stop`. So to avoid +deadlocks you must treat :c:func:`jbd2_journal_start` / +:c:func:`jbd2_journal_stop` as if they were semaphores and include them in +your semaphore ordering rules to prevent +deadlocks. Note that :c:func:`jbd2_journal_extend` has similar blocking +behaviour to :c:func:`jbd2_journal_start` so you can deadlock here just as +easily as on :c:func:`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 @@ -222,13 +225,14 @@ 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 +``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 +``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 +:c:func:`jbd2_journal_lock_updates()` / +:c:func:`jbd2_journal_unlock_updates()`. Ext4 uses this when it wants a window with a clean and stable fs for a moment. E.g. :: -- cgit From 76d0d5d3136381e60bb8674d995f74bdb9085c2f Mon Sep 17 00:00:00 2001 From: Mauro Carvalho Chehab Date: Fri, 12 May 2017 07:27:13 -0300 Subject: docs-rst: don't ignore internal functions for jbd2 docs Those functions are currently ignored, causing references at the documentation to be lost. Don't ignore it. Signed-off-by: Mauro Carvalho Chehab --- Documentation/filesystems/index.rst | 1 - 1 file changed, 1 deletion(-) (limited to 'Documentation/filesystems') diff --git a/Documentation/filesystems/index.rst b/Documentation/filesystems/index.rst index 148becd91cba..256e10eedba4 100644 --- a/Documentation/filesystems/index.rst +++ b/Documentation/filesystems/index.rst @@ -287,7 +287,6 @@ Transasction Level ~~~~~~~~~~~~~~~~~~ .. kernel-doc:: fs/jbd2/transaction.c - :export: See also -------- -- cgit From 3db38ed76890565772fcca3279cc8d454ea6176b Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Sat, 13 May 2017 04:51:52 -0700 Subject: doc: ReSTify keys-request-key.txt Adjusts for ReST markup and moves under keys security devel index. Cc: David Howells Signed-off-by: Kees Cook Signed-off-by: Jonathan Corbet --- Documentation/filesystems/nfs/idmapper.txt | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'Documentation/filesystems') diff --git a/Documentation/filesystems/nfs/idmapper.txt b/Documentation/filesystems/nfs/idmapper.txt index fe03d10bb79a..b86831acd583 100644 --- a/Documentation/filesystems/nfs/idmapper.txt +++ b/Documentation/filesystems/nfs/idmapper.txt @@ -55,7 +55,7 @@ request-key will find the first matching line and corresponding program. In this case, /some/other/program will handle all uid lookups and /usr/sbin/nfs.idmap will handle gid, user, and group lookups. -See for more information +See for more information about the request-key function. -- cgit