Linux Kernel Procfs Guide | ||
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Instead of reading (or writing) information directly from
kernel memory, procfs works with call back
functions for files: functions that are called when
a specific file is being read or written. Such functions have
to be initialised after the procfs file is created by setting
the read_proc
and/or
write_proc
fields in the
struct proc_dir_entry*
that the
function create_proc_entry returned:
struct proc_dir_entry* entry; entry->read_proc = read_proc_foo; entry->write_proc = write_proc_foo; |
If you only want to use a the
read_proc
, the function
create_proc_read_entry described in the Section called Convenience functions in the chapter called Tips and tricks may be used to create and initialise the
procfs entry in one single call.
The read function is a call back function that allows userland processes to read data from the kernel. The read function should have the following format:
The read function should write its information into the page. For proper use, the function should start writing at an offset of off in page and write at most count 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 more and less, but cat still works).
If the off and count parameters are properly used, eof should be used to signal that the end of the file has been reached by writing 1 to the memory location eof points to.
The parameter start doesn't seem to be used anywhere in the kernel. The data parameter can be used to create a single call back function for several files, see the Section called A single call back for many files.
The read_func function must return the number of bytes written into the page.
the chapter called Example shows how to use a read call back function.
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Removing an entry | Writing data |