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authorTakashi Iwai <tiwai@suse.de>2010-04-13 10:55:09 (GMT)
committerTakashi Iwai <tiwai@suse.de>2010-04-13 10:55:09 (GMT)
commitc56a3b18475b0f93b484c25162c1379f5aee367a (patch)
tree0735b26f5d27934cbf52a12e22743bbe85ac68b8 /Documentation/DocBook
parent02f4865fa415a87de28cc8c2e4d798ff46be1cf8 (diff)
ALSA: Update the documentation for changes of proc files
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Diffstat (limited to 'Documentation/DocBook')
-rw-r--r--Documentation/DocBook/writing-an-alsa-driver.tmpl27
1 files changed, 17 insertions, 10 deletions
diff --git a/Documentation/DocBook/writing-an-alsa-driver.tmpl b/Documentation/DocBook/writing-an-alsa-driver.tmpl
index 0d0f7b4..0ba149d 100644
--- a/Documentation/DocBook/writing-an-alsa-driver.tmpl
+++ b/Documentation/DocBook/writing-an-alsa-driver.tmpl
@@ -5518,34 +5518,41 @@ struct _snd_pcm_runtime {
]]>
</programlisting>
</informalexample>
+
+ For the raw data, <structfield>size</structfield> field must be
+ set properly. This specifies the maximum size of the proc file access.
</para>
<para>
- The callback is much more complicated than the text-file
- version. You need to use a low-level I/O functions such as
+ The read/write callbacks of raw mode are more direct than the text mode.
+ You need to use a low-level I/O functions such as
<function>copy_from/to_user()</function> to transfer the
data.
<informalexample>
<programlisting>
<![CDATA[
- static long my_file_io_read(struct snd_info_entry *entry,
+ static ssize_t my_file_io_read(struct snd_info_entry *entry,
void *file_private_data,
struct file *file,
char *buf,
- unsigned long count,
- unsigned long pos)
+ size_t count,
+ loff_t pos)
{
- long size = count;
- if (pos + size > local_max_size)
- size = local_max_size - pos;
- if (copy_to_user(buf, local_data + pos, size))
+ if (copy_to_user(buf, local_data + pos, count))
return -EFAULT;
- return size;
+ return count;
}
]]>
</programlisting>
</informalexample>
+
+ If the size of the info entry has been set up properly,
+ <structfield>count</structfield> and <structfield>pos</structfield> are
+ guaranteed to fit within 0 and the given size.
+ You don't have to check the range in the callbacks unless any
+ other condition is required.
+
</para>
</chapter>

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