Commit 7caf3e3f authored by Puranjay Mohan's avatar Puranjay Mohan Committed by Jonathan Corbet

Filesystems: Documentation: Replace deprecated :c:func: Usage

Replace :c:func: with func() as the previous usage is deprecated.
Signed-off-by: default avatarPuranjay Mohan <puranjay12@gmail.com>
Link: https://lore.kernel.org/r/20200810184828.29297-1-puranjay12@gmail.comSigned-off-by: default avatarJonathan Corbet <corbet@lwn.net>
parent 1fc0fd67
...@@ -10,27 +10,27 @@ Details ...@@ -10,27 +10,27 @@ Details
The journalling layer is easy to use. You need to first of all create a 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 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 how you decide to allocate the physical media on which the journal
resides. The :c:func:`jbd2_journal_init_inode` call is for journals stored in resides. The jbd2_journal_init_inode() call is for journals stored in
filesystem inodes, or the :c:func:`jbd2_journal_init_dev` call can be used 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 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 journal_t is a typedef for a struct pointer, so when you are finally
finished make sure you call :c:func:`jbd2_journal_destroy` on it to free up finished make sure you call jbd2_journal_destroy() on it to free up
any used kernel memory. any used kernel memory.
Once you have got your journal_t object you need to 'mount' or load the 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 journal file. The journalling layer expects the space for the journal
was already allocated and initialized properly by the userspace tools. was already allocated and initialized properly by the userspace tools.
When loading the journal you must call :c:func:`jbd2_journal_load` to process When loading the journal you must call jbd2_journal_load() to process
journal contents. If the client file system detects the journal contents 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 does not need to be processed (or even need not have valid contents), it
may call :c:func:`jbd2_journal_wipe` to clear the journal contents before may call jbd2_journal_wipe() to clear the journal contents before
calling :c:func:`jbd2_journal_load`. calling jbd2_journal_load().
Note that jbd2_journal_wipe(..,0) calls Note that jbd2_journal_wipe(..,0) calls
:c:func:`jbd2_journal_skip_recovery` for you if it detects any outstanding jbd2_journal_skip_recovery() for you if it detects any outstanding
transactions in the journal and similarly :c:func:`jbd2_journal_load` will transactions in the journal and similarly jbd2_journal_load() will
call :c:func:`jbd2_journal_recover` if necessary. I would advise reading call jbd2_journal_recover() if necessary. I would advise reading
:c:func:`ext4_load_journal` in fs/ext4/super.c for examples on this stage. ext4_load_journal() in fs/ext4/super.c for examples on this stage.
Now you can go ahead and start modifying the underlying filesystem. Now you can go ahead and start modifying the underlying filesystem.
Almost. Almost.
...@@ -39,57 +39,57 @@ You still need to actually journal your filesystem changes, this is done ...@@ -39,57 +39,57 @@ You still need to actually journal your filesystem changes, this is done
by wrapping them into transactions. Additionally you also need to wrap by wrapping them into transactions. Additionally you also need to wrap
the modification of each of the buffers with calls to the journal layer, 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 so it knows what the modifications you are actually making are. To do
this use :c:func:`jbd2_journal_start` which returns a transaction handle. this use jbd2_journal_start() which returns a transaction handle.
:c:func:`jbd2_journal_start` and its counterpart :c:func:`jbd2_journal_stop`, jbd2_journal_start() and its counterpart jbd2_journal_stop(),
which indicates the end of a transaction are nestable calls, so you can which indicates the end of a transaction are nestable calls, so you can
reenter a transaction if necessary, but remember you must call reenter a transaction if necessary, but remember you must call
:c:func:`jbd2_journal_stop` the same number of times as jbd2_journal_stop() the same number of times as
:c:func:`jbd2_journal_start` before the transaction is completed (or more jbd2_journal_start() before the transaction is completed (or more
accurately leaves the update phase). Ext4/VFS makes use of this feature to accurately leaves the update phase). Ext4/VFS makes use of this feature to
simplify handling of inode dirtying, quota support, etc. simplify handling of inode dirtying, quota support, etc.
Inside each transaction you need to wrap the modifications to the Inside each transaction you need to wrap the modifications to the
individual buffers (blocks). Before you start to modify a buffer you individual buffers (blocks). Before you start to modify a buffer you
need to call :c:func:`jbd2_journal_get_create_access()` / need to call jbd2_journal_get_create_access() /
:c:func:`jbd2_journal_get_write_access()` / jbd2_journal_get_write_access() /
:c:func:`jbd2_journal_get_undo_access()` as appropriate, this allows the jbd2_journal_get_undo_access() as appropriate, this allows the
journalling layer to copy the unmodified journalling layer to copy the unmodified
data if it needs to. After all the buffer may be part of a previously 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 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 buffer, and once you are have done so you need to call
:c:func:`jbd2_journal_dirty_metadata`. Or if you've asked for access to a 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 buffer you now know is now longer required to be pushed back on the
device you can call :c:func:`jbd2_journal_forget` in much the same way as you device you can call jbd2_journal_forget() in much the same way as you
might have used :c:func:`bforget` in the past. might have used bforget() in the past.
A :c:func:`jbd2_journal_flush` may be called at any time to commit and A jbd2_journal_flush() may be called at any time to commit and
checkpoint all your transactions. checkpoint all your transactions.
Then at umount time , in your :c:func:`put_super` you can then call Then at umount time , in your put_super() you can then call
:c:func:`jbd2_journal_destroy` to clean up your in-core journal object. jbd2_journal_destroy() to clean up your in-core journal object.
Unfortunately there a couple of ways the journal layer can cause a 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 deadlock. The first thing to note is that each task can only have a
single outstanding transaction at any one time, remember nothing commits single outstanding transaction at any one time, remember nothing commits
until the outermost :c:func:`jbd2_journal_stop`. This means you must complete until the outermost jbd2_journal_stop(). This means you must complete
the transaction at the end of each file/inode/address etc. operation you 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 perform, so that the journalling system isn't re-entered on another
journal. Since transactions can't be nested/batched across differing journal. Since transactions can't be nested/batched across differing
journals, and another filesystem other than yours (say ext4) may be journals, and another filesystem other than yours (say ext4) may be
modified in a later syscall. modified in a later syscall.
The second case to bear in mind is that :c:func:`jbd2_journal_start` can block 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 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 on the passed nblocks param) - when it blocks it merely(!) needs to wait
for transactions to complete and be committed from other tasks, so for transactions to complete and be committed from other tasks, so
essentially we are waiting for :c:func:`jbd2_journal_stop`. So to avoid essentially we are waiting for jbd2_journal_stop(). So to avoid
deadlocks you must treat :c:func:`jbd2_journal_start` / deadlocks you must treat jbd2_journal_start() /
:c:func:`jbd2_journal_stop` as if they were semaphores and include them in jbd2_journal_stop() as if they were semaphores and include them in
your semaphore ordering rules to prevent your semaphore ordering rules to prevent
deadlocks. Note that :c:func:`jbd2_journal_extend` has similar blocking deadlocks. Note that jbd2_journal_extend() has similar blocking
behaviour to :c:func:`jbd2_journal_start` so you can deadlock here just as behaviour to jbd2_journal_start() so you can deadlock here just as
easily as on :c:func:`jbd2_journal_start`. easily as on jbd2_journal_start().
Try to reserve the right number of blocks the first time. ;-). This will 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 be the maximum number of blocks you are going to touch in this
...@@ -116,8 +116,8 @@ called after each transaction commit. You can also use ...@@ -116,8 +116,8 @@ called after each transaction commit. You can also use
that need processing when the transaction commits. that need processing when the transaction commits.
JBD2 also provides a way to block all transaction updates via JBD2 also provides a way to block all transaction updates via
:c:func:`jbd2_journal_lock_updates()` / jbd2_journal_lock_updates() /
:c:func:`jbd2_journal_unlock_updates()`. Ext4 uses this when it wants a jbd2_journal_unlock_updates(). Ext4 uses this when it wants a
window with a clean and stable fs for a moment. E.g. window with a clean and stable fs for a moment. E.g.
:: ::
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