Merge branch 'docs' of git://git.lwn.net/linux-2.6

* 'docs' of git://git.lwn.net/linux-2.6:
  Add additional examples in Documentation/spinlocks.txt
  Move sched-rt-group.txt to scheduler/
  Documentation: move rpc-cache.txt to filesystems/
  Documentation: move nfsroot.txt to filesystems/
  Spell out behavior of atomic_dec_and_lock() in kerneldoc
  Fix a typo in highres.txt
  Fixes to the seq_file document
  Fill out information on patch tags in SubmittingPatches
  Add the seq_file documentation
This commit is contained in:
Linus Torvalds 2008-04-11 13:24:16 -07:00
commit 14897e35fd
15 changed files with 380 additions and 20 deletions

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@ -271,8 +271,6 @@ netlabel/
- directory with information on the NetLabel subsystem.
networking/
- directory with info on various aspects of networking with Linux.
nfsroot.txt
- short guide on setting up a diskless box with NFS root filesystem.
nmi_watchdog.txt
- info on NMI watchdog for SMP systems.
nommu-mmap.txt
@ -321,8 +319,6 @@ robust-futexes.txt
- a description of what robust futexes are.
rocket.txt
- info on the Comtrol RocketPort multiport serial driver.
rpc-cache.txt
- introduction to the caching mechanisms in the sunrpc layer.
rt-mutex-design.txt
- description of the RealTime mutex implementation design.
rt-mutex.txt

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@ -328,7 +328,7 @@ now, but you can do this to mark internal company procedures or just
point out some special detail about the sign-off.
13) When to use Acked-by:
13) When to use Acked-by: and Cc:
The Signed-off-by: tag indicates that the signer was involved in the
development of the patch, or that he/she was in the patch's delivery path.
@ -349,11 +349,59 @@ Acked-by: does not necessarily indicate acknowledgement of the entire patch.
For example, if a patch affects multiple subsystems and has an Acked-by: from
one subsystem maintainer then this usually indicates acknowledgement of just
the part which affects that maintainer's code. Judgement should be used here.
When in doubt people should refer to the original discussion in the mailing
When in doubt people should refer to the original discussion in the mailing
list archives.
If a person has had the opportunity to comment on a patch, but has not
provided such comments, you may optionally add a "Cc:" tag to the patch.
This is the only tag which might be added without an explicit action by the
person it names. This tag documents that potentially interested parties
have been included in the discussion
14) The canonical patch format
14) Using Test-by: and Reviewed-by:
A Tested-by: tag indicates that the patch has been successfully tested (in
some environment) by the person named. This tag informs maintainers that
some testing has been performed, provides a means to locate testers for
future patches, and ensures credit for the testers.
Reviewed-by:, instead, indicates that the patch has been reviewed and found
acceptable according to the Reviewer's Statement:
Reviewer's statement of oversight
By offering my Reviewed-by: tag, I state that:
(a) I have carried out a technical review of this patch to
evaluate its appropriateness and readiness for inclusion into
the mainline kernel.
(b) Any problems, concerns, or questions relating to the patch
have been communicated back to the submitter. I am satisfied
with the submitter's response to my comments.
(c) While there may be things that could be improved with this
submission, I believe that it is, at this time, (1) a
worthwhile modification to the kernel, and (2) free of known
issues which would argue against its inclusion.
(d) While I have reviewed the patch and believe it to be sound, I
do not (unless explicitly stated elsewhere) make any
warranties or guarantees that it will achieve its stated
purpose or function properly in any given situation.
A Reviewed-by tag is a statement of opinion that the patch is an
appropriate modification of the kernel without any remaining serious
technical issues. Any interested reviewer (who has done the work) can
offer a Reviewed-by tag for a patch. This tag serves to give credit to
reviewers and to inform maintainers of the degree of review which has been
done on the patch. Reviewed-by: tags, when supplied by reviewers known to
understand the subject area and to perform thorough reviews, will normally
increase the liklihood of your patch getting into the kernel.
15) The canonical patch format
The canonical patch subject line is:

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@ -66,6 +66,8 @@ mandatory-locking.txt
- info on the Linux implementation of Sys V mandatory file locking.
ncpfs.txt
- info on Novell Netware(tm) filesystem using NCP protocol.
nfsroot.txt
- short guide on setting up a diskless box with NFS root filesystem.
ntfs.txt
- info and mount options for the NTFS filesystem (Windows NT).
ocfs2.txt
@ -82,6 +84,10 @@ relay.txt
- info on relay, for efficient streaming from kernel to user space.
romfs.txt
- description of the ROMFS filesystem.
rpc-cache.txt
- introduction to the caching mechanisms in the sunrpc layer.
seq_file.txt
- how to use the seq_file API
sharedsubtree.txt
- a description of shared subtrees for namespaces.
smbfs.txt

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@ -0,0 +1,283 @@
The seq_file interface
Copyright 2003 Jonathan Corbet <corbet@lwn.net>
This file is originally from the LWN.net Driver Porting series at
http://lwn.net/Articles/driver-porting/
There are numerous ways for a device driver (or other kernel component) to
provide information to the user or system administrator. One useful
technique is the creation of virtual files, in debugfs, /proc or elsewhere.
Virtual files can provide human-readable output that is easy to get at
without any special utility programs; they can also make life easier for
script writers. It is not surprising that the use of virtual files has
grown over the years.
Creating those files correctly has always been a bit of a challenge,
however. It is not that hard to make a virtual file which returns a
string. But life gets trickier if the output is long - anything greater
than an application is likely to read in a single operation. Handling
multiple reads (and seeks) requires careful attention to the reader's
position within the virtual file - that position is, likely as not, in the
middle of a line of output. The kernel has traditionally had a number of
implementations that got this wrong.
The 2.6 kernel contains a set of functions (implemented by Alexander Viro)
which are designed to make it easy for virtual file creators to get it
right.
The seq_file interface is available via <linux/seq_file.h>. There are
three aspects to seq_file:
* An iterator interface which lets a virtual file implementation
step through the objects it is presenting.
* Some utility functions for formatting objects for output without
needing to worry about things like output buffers.
* A set of canned file_operations which implement most operations on
the virtual file.
We'll look at the seq_file interface via an extremely simple example: a
loadable module which creates a file called /proc/sequence. The file, when
read, simply produces a set of increasing integer values, one per line. The
sequence will continue until the user loses patience and finds something
better to do. The file is seekable, in that one can do something like the
following:
dd if=/proc/sequence of=out1 count=1
dd if=/proc/sequence skip=1 out=out2 count=1
Then concatenate the output files out1 and out2 and get the right
result. Yes, it is a thoroughly useless module, but the point is to show
how the mechanism works without getting lost in other details. (Those
wanting to see the full source for this module can find it at
http://lwn.net/Articles/22359/).
The iterator interface
Modules implementing a virtual file with seq_file must implement a simple
iterator object that allows stepping through the data of interest.
Iterators must be able to move to a specific position - like the file they
implement - but the interpretation of that position is up to the iterator
itself. A seq_file implementation that is formatting firewall rules, for
example, could interpret position N as the Nth rule in the chain.
Positioning can thus be done in whatever way makes the most sense for the
generator of the data, which need not be aware of how a position translates
to an offset in the virtual file. The one obvious exception is that a
position of zero should indicate the beginning of the file.
The /proc/sequence iterator just uses the count of the next number it
will output as its position.
Four functions must be implemented to make the iterator work. The first,
called start() takes a position as an argument and returns an iterator
which will start reading at that position. For our simple sequence example,
the start() function looks like:
static void *ct_seq_start(struct seq_file *s, loff_t *pos)
{
loff_t *spos = kmalloc(sizeof(loff_t), GFP_KERNEL);
if (! spos)
return NULL;
*spos = *pos;
return spos;
}
The entire data structure for this iterator is a single loff_t value
holding the current position. There is no upper bound for the sequence
iterator, but that will not be the case for most other seq_file
implementations; in most cases the start() function should check for a
"past end of file" condition and return NULL if need be.
For more complicated applications, the private field of the seq_file
structure can be used. There is also a special value whch can be returned
by the start() function called SEQ_START_TOKEN; it can be used if you wish
to instruct your show() function (described below) to print a header at the
top of the output. SEQ_START_TOKEN should only be used if the offset is
zero, however.
The next function to implement is called, amazingly, next(); its job is to
move the iterator forward to the next position in the sequence. The
example module can simply increment the position by one; more useful
modules will do what is needed to step through some data structure. The
next() function returns a new iterator, or NULL if the sequence is
complete. Here's the example version:
static void *ct_seq_next(struct seq_file *s, void *v, loff_t *pos)
{
loff_t *spos = v;
*pos = ++*spos;
return spos;
}
The stop() function is called when iteration is complete; its job, of
course, is to clean up. If dynamic memory is allocated for the iterator,
stop() is the place to free it.
static void ct_seq_stop(struct seq_file *s, void *v)
{
kfree(v);
}
Finally, the show() function should format the object currently pointed to
by the iterator for output. It should return zero, or an error code if
something goes wrong. The example module's show() function is:
static int ct_seq_show(struct seq_file *s, void *v)
{
loff_t *spos = v;
seq_printf(s, "%lld\n", (long long)*spos);
return 0;
}
We will look at seq_printf() in a moment. But first, the definition of the
seq_file iterator is finished by creating a seq_operations structure with
the four functions we have just defined:
static const struct seq_operations ct_seq_ops = {
.start = ct_seq_start,
.next = ct_seq_next,
.stop = ct_seq_stop,
.show = ct_seq_show
};
This structure will be needed to tie our iterator to the /proc file in
a little bit.
It's worth noting that the interator value returned by start() and
manipulated by the other functions is considered to be completely opaque by
the seq_file code. It can thus be anything that is useful in stepping
through the data to be output. Counters can be useful, but it could also be
a direct pointer into an array or linked list. Anything goes, as long as
the programmer is aware that things can happen between calls to the
iterator function. However, the seq_file code (by design) will not sleep
between the calls to start() and stop(), so holding a lock during that time
is a reasonable thing to do. The seq_file code will also avoid taking any
other locks while the iterator is active.
Formatted output
The seq_file code manages positioning within the output created by the
iterator and getting it into the user's buffer. But, for that to work, that
output must be passed to the seq_file code. Some utility functions have
been defined which make this task easy.
Most code will simply use seq_printf(), which works pretty much like
printk(), but which requires the seq_file pointer as an argument. It is
common to ignore the return value from seq_printf(), but a function
producing complicated output may want to check that value and quit if
something non-zero is returned; an error return means that the seq_file
buffer has been filled and further output will be discarded.
For straight character output, the following functions may be used:
int seq_putc(struct seq_file *m, char c);
int seq_puts(struct seq_file *m, const char *s);
int seq_escape(struct seq_file *m, const char *s, const char *esc);
The first two output a single character and a string, just like one would
expect. seq_escape() is like seq_puts(), except that any character in s
which is in the string esc will be represented in octal form in the output.
There is also a function for printing filenames:
int seq_path(struct seq_file *m, struct path *path, char *esc);
Here, path indicates the file of interest, and esc is a set of characters
which should be escaped in the output.
Making it all work
So far, we have a nice set of functions which can produce output within the
seq_file system, but we have not yet turned them into a file that a user
can see. Creating a file within the kernel requires, of course, the
creation of a set of file_operations which implement the operations on that
file. The seq_file interface provides a set of canned operations which do
most of the work. The virtual file author still must implement the open()
method, however, to hook everything up. The open function is often a single
line, as in the example module:
static int ct_open(struct inode *inode, struct file *file)
{
return seq_open(file, &ct_seq_ops);
}
Here, the call to seq_open() takes the seq_operations structure we created
before, and gets set up to iterate through the virtual file.
On a successful open, seq_open() stores the struct seq_file pointer in
file->private_data. If you have an application where the same iterator can
be used for more than one file, you can store an arbitrary pointer in the
private field of the seq_file structure; that value can then be retrieved
by the iterator functions.
The other operations of interest - read(), llseek(), and release() - are
all implemented by the seq_file code itself. So a virtual file's
file_operations structure will look like:
static const struct file_operations ct_file_ops = {
.owner = THIS_MODULE,
.open = ct_open,
.read = seq_read,
.llseek = seq_lseek,
.release = seq_release
};
There is also a seq_release_private() which passes the contents of the
seq_file private field to kfree() before releasing the structure.
The final step is the creation of the /proc file itself. In the example
code, that is done in the initialization code in the usual way:
static int ct_init(void)
{
struct proc_dir_entry *entry;
entry = create_proc_entry("sequence", 0, NULL);
if (entry)
entry->proc_fops = &ct_file_ops;
return 0;
}
module_init(ct_init);
And that is pretty much it.
seq_list
If your file will be iterating through a linked list, you may find these
routines useful:
struct list_head *seq_list_start(struct list_head *head,
loff_t pos);
struct list_head *seq_list_start_head(struct list_head *head,
loff_t pos);
struct list_head *seq_list_next(void *v, struct list_head *head,
loff_t *ppos);
These helpers will interpret pos as a position within the list and iterate
accordingly. Your start() and next() functions need only invoke the
seq_list_* helpers with a pointer to the appropriate list_head structure.
The extra-simple version
For extremely simple virtual files, there is an even easier interface. A
module can define only the show() function, which should create all the
output that the virtual file will contain. The file's open() method then
calls:
int single_open(struct file *file,
int (*show)(struct seq_file *m, void *p),
void *data);
When output time comes, the show() function will be called once. The data
value given to single_open() can be found in the private field of the
seq_file structure. When using single_open(), the programmer should use
single_release() instead of seq_release() in the file_operations structure
to avoid a memory leak.

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@ -98,7 +98,7 @@ System-level global event devices are used for the Linux periodic tick. Per-CPU
event devices are used to provide local CPU functionality such as process
accounting, profiling, and high resolution timers.
The management layer assignes one or more of the folliwing functions to a clock
The management layer assigns one or more of the following functions to a clock
event device:
- system global periodic tick (jiffies update)
- cpu local update_process_times

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@ -844,7 +844,7 @@ and is between 256 and 4096 characters. It is defined in the file
arch/alpha/kernel/core_marvel.c.
ip= [IP_PNP]
See Documentation/nfsroot.txt.
See Documentation/filesystems/nfsroot.txt.
ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
See comment before ip2_setup() in
@ -1198,10 +1198,10 @@ and is between 256 and 4096 characters. It is defined in the file
file if at all.
nfsaddrs= [NFS]
See Documentation/nfsroot.txt.
See Documentation/filesystems/nfsroot.txt.
nfsroot= [NFS] nfs root filesystem for disk-less boxes.
See Documentation/nfsroot.txt.
See Documentation/filesystems/nfsroot.txt.
nfs.callback_tcpport=
[NFS] set the TCP port on which the NFSv4 callback

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@ -12,5 +12,7 @@ sched-domains.txt
- information on scheduling domains.
sched-nice-design.txt
- How and why the scheduler's nice levels are implemented.
sched-rt-group.txt
- real-time group scheduling.
sched-stats.txt
- information on schedstats (Linux Scheduler Statistics).

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@ -5,6 +5,28 @@ Please use DEFINE_SPINLOCK()/DEFINE_RWLOCK() or
__SPIN_LOCK_UNLOCKED()/__RW_LOCK_UNLOCKED() as appropriate for static
initialization.
Most of the time, you can simply turn:
static spinlock_t xxx_lock = SPIN_LOCK_UNLOCKED;
into:
static DEFINE_SPINLOCK(xxx_lock);
Static structure member variables go from:
struct foo bar {
.lock = SPIN_LOCK_UNLOCKED;
};
to:
struct foo bar {
.lock = __SPIN_LOCK_UNLOCKED(bar.lock);
};
Declaration of static rw_locks undergo a similar transformation.
Dynamic initialization, when necessary, may be performed as
demonstrated below.

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@ -1744,10 +1744,10 @@ config ROOT_NFS
If you want your Linux box to mount its whole root file system (the
one containing the directory /) from some other computer over the
net via NFS (presumably because your box doesn't have a hard disk),
say Y. Read <file:Documentation/nfsroot.txt> for details. It is
likely that in this case, you also want to say Y to "Kernel level IP
autoconfiguration" so that your box can discover its network address
at boot time.
say Y. Read <file:Documentation/filesystems/nfsroot.txt> for
details. It is likely that in this case, you also want to say Y to
"Kernel level IP autoconfiguration" so that your box can discover
its network address at boot time.
Most people say N here.

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@ -341,6 +341,9 @@ static inline void double_spin_unlock(spinlock_t *l1, spinlock_t *l2,
* atomic_dec_and_lock - lock on reaching reference count zero
* @atomic: the atomic counter
* @lock: the spinlock in question
*
* Decrements @atomic by 1. If the result is 0, returns true and locks
* @lock. Returns false for all other cases.
*/
extern int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock);
#define atomic_dec_and_lock(atomic, lock) \

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@ -160,7 +160,7 @@ config IP_PNP_DHCP
If unsure, say Y. Note that if you want to use DHCP, a DHCP server
must be operating on your network. Read
<file:Documentation/nfsroot.txt> for details.
<file:Documentation/filesystems/nfsroot.txt> for details.
config IP_PNP_BOOTP
bool "IP: BOOTP support"
@ -175,7 +175,7 @@ config IP_PNP_BOOTP
does BOOTP itself, providing all necessary information on the kernel
command line, you can say N here. If unsure, say Y. Note that if you
want to use BOOTP, a BOOTP server must be operating on your network.
Read <file:Documentation/nfsroot.txt> for details.
Read <file:Documentation/filesystems/nfsroot.txt> for details.
config IP_PNP_RARP
bool "IP: RARP support"
@ -187,8 +187,8 @@ config IP_PNP_RARP
discovered automatically at boot time using the RARP protocol (an
older protocol which is being obsoleted by BOOTP and DHCP), say Y
here. Note that if you want to use RARP, a RARP server must be
operating on your network. Read <file:Documentation/nfsroot.txt> for
details.
operating on your network. Read
<file:Documentation/filesystems/nfsroot.txt> for details.
# not yet ready..
# bool ' IP: ARP support' CONFIG_IP_PNP_ARP

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@ -1411,7 +1411,7 @@ late_initcall(ip_auto_config);
/*
* Decode any IP configuration options in the "ip=" or "nfsaddrs=" kernel
* command line parameter. See Documentation/nfsroot.txt.
* command line parameter. See Documentation/filesystems/nfsroot.txt.
*/
static int __init ic_proto_name(char *name)
{