diff options
Diffstat (limited to 'Documentation/DocBook')
| -rw-r--r-- | Documentation/DocBook/procfs-guide.tmpl | 82 |
1 files changed, 63 insertions, 19 deletions
diff --git a/Documentation/DocBook/procfs-guide.tmpl b/Documentation/DocBook/procfs-guide.tmpl index 45cad23..2de84dc 100644 --- a/Documentation/DocBook/procfs-guide.tmpl +++ b/Documentation/DocBook/procfs-guide.tmpl @@ -352,49 +352,93 @@ entry->write_proc = write_proc_foo; <funcsynopsis> <funcprototype> <funcdef>int <function>read_func</function></funcdef> - <paramdef>char* <parameter>page</parameter></paramdef> + <paramdef>char* <parameter>buffer</parameter></paramdef> <paramdef>char** <parameter>start</parameter></paramdef> <paramdef>off_t <parameter>off</parameter></paramdef> <paramdef>int <parameter>count</parameter></paramdef> - <paramdef>int* <parameter>eof</parameter></paramdef> + <paramdef>int* <parameter>peof</parameter></paramdef> <paramdef>void* <parameter>data</parameter></paramdef> </funcprototype> </funcsynopsis> <para> The read function should write its information into the - <parameter>page</parameter>. For proper use, the function - should start writing at an offset of - <parameter>off</parameter> in <parameter>page</parameter> and - write at most <parameter>count</parameter> bytes, but because - most read functions are quite simple and only return a small - amount of information, these two parameters are usually - ignored (it breaks pagers like <literal>more</literal> and - <literal>less</literal>, but <literal>cat</literal> still - works). + <parameter>buffer</parameter>, which will be exactly + <literal>PAGE_SIZE</literal> bytes long. </para> <para> - If the <parameter>off</parameter> and - <parameter>count</parameter> parameters are properly used, - <parameter>eof</parameter> should be used to signal that the + The parameter + <parameter>peof</parameter> should be used to signal that the end of the file has been reached by writing <literal>1</literal> to the memory location - <parameter>eof</parameter> points to. + <parameter>peof</parameter> points to. </para> <para> - The parameter <parameter>start</parameter> doesn't seem to be - used anywhere in the kernel. The <parameter>data</parameter> + The <parameter>data</parameter> parameter can be used to create a single call back function for several files, see <xref linkend="usingdata"/>. </para> <para> - The <function>read_func</function> function must return the - number of bytes written into the <parameter>page</parameter>. + The rest of the parameters and the return value are described + by a comment in <filename>fs/proc/generic.c</filename> as follows: </para> + <blockquote> + <para> + You have three ways to return data: + </para> + <orderedlist> + <listitem> + <para> + Leave <literal>*start = NULL</literal>. (This is the default.) + Put the data of the requested offset at that + offset within the buffer. Return the number (<literal>n</literal>) + of bytes there are from the beginning of the + buffer up to the last byte of data. If the + number of supplied bytes (<literal>= n - offset</literal>) is + greater than zero and you didn't signal eof + and the reader is prepared to take more data + you will be called again with the requested + offset advanced by the number of bytes + absorbed. This interface is useful for files + no larger than the buffer. + </para> + </listitem> + <listitem> + <para> + Set <literal>*start</literal> to an unsigned long value less than + the buffer address but greater than zero. + Put the data of the requested offset at the + beginning of the buffer. Return the number of + bytes of data placed there. If this number is + greater than zero and you didn't signal eof + and the reader is prepared to take more data + you will be called again with the requested + offset advanced by <literal>*start</literal>. This interface is + useful when you have a large file consisting + of a series of blocks which you want to count + and return as wholes. + (Hack by Paul.Russell@rustcorp.com.au) + </para> + </listitem> + <listitem> + <para> + Set <literal>*start</literal> to an address within the buffer. + Put the data of the requested offset at <literal>*start</literal>. + Return the number of bytes of data placed there. + If this number is greater than zero and you + didn't signal eof and the reader is prepared to + take more data you will be called again with the + requested offset advanced by the number of bytes + absorbed. + </para> + </listitem> + </orderedlist> + </blockquote> + <para> <xref linkend="example"/> shows how to use a read call back function. |
