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author | Takashi Iwai <tiwai@suse.de> | 2010-04-13 12:55:09 +0200 |
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committer | Takashi Iwai <tiwai@suse.de> | 2010-04-13 12:55:09 +0200 |
commit | c56a3b18475b0f93b484c25162c1379f5aee367a (patch) | |
tree | 0735b26f5d27934cbf52a12e22743bbe85ac68b8 | |
parent | 02f4865fa415a87de28cc8c2e4d798ff46be1cf8 (diff) | |
download | linux-c56a3b18475b0f93b484c25162c1379f5aee367a.tar.bz2 |
ALSA: Update the documentation for changes of proc files
Signed-off-by: Takashi Iwai <tiwai@suse.de>
-rw-r--r-- | Documentation/DocBook/writing-an-alsa-driver.tmpl | 27 |
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 0d0f7b4d4b1a..0ba149de2608 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> |