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Nothing really special, but here is the simplest place to keep it, especially as others may need it too. git-svn-id: http://lm-sensors.org/svn/lm-sensors/trunk@152 7894878c-1315-0410-8ee3-d5d059ff63e0
146 lines
5.5 KiB
Plaintext
146 lines
5.5 KiB
Plaintext
This file documents how to handle the callback function that returns the
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information displayed in a (non-/proc/sys) /proc file.
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For kernels before 2.1.29, you have to declare a proc_dir_entry, with
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in the get_info field the procedure handler. For kernels 2.1.29 and later,
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you can use the create_proc_entry function and assign a new value (the
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procedure handler address) to the read_proc field:
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#if LINUX_VERSION_CODE < KERNEL_VERSION(2,1,29)
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static int read_bus_i2c(char *buf, char **start, off_t offset, int len,
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int unused);
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static struct proc_dir_entry proc_bus_i2c_dir =
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{
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/* low_ino */ 0, /* Set by proc_register_dynamic */
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/* namelen */ 3, /* The length of the name field */
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/* name */ "i2c",
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/* mode */ S_IRUGO | S_IFREG,
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/* nlink */ 1,
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/* uid */ 0,
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/* gid */ 0,
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/* size */ 0,
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/* ops */ NULL,
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/* get_info */ &read_bus_i2c
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};
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#else /* LINUX_VERSION_CODE >= KERNEL_VERSION(2,1,29)
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static int read_bus_i2c(char *buf, char **start, off_t offset, int len,
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int *eof , void *private);
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#endif
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/* This code fragment is part of the initialization code. You should do
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several safety checks, like whether create_proc_entry does not return
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NULL. */
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#if LINUX_VERSION_CODE < KERNEL_VERSION(2,1,29)
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proc_register_dynamic(&proc_root, &proc_bus_i2c_dir);
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#else /* LINUX_VERSION_CODE >= KERNEL_VERSION(2,1,29)
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proc_bus_i2c = create_proc_entry("i2c",0,proc_root);
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proc_bus_i2c->read_proc = &read_bus_i2c;
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#endif
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Now for the function itself.
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LINUX KERNEL 2.0.x, and 2.1.x upto 2.1.28
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=========================================
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This function is known as the get_info function.
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int get_info(char *buf, char **start, off_t offset, int len, int unused);
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(INPUT)
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buf: A kernel-space buffer where we can put the information.
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len: The buffer length (we have a bit of slack here: if we write
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'a little' beyond this, things will still work out)
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(OUTPUT)
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*buf: The complete contents of the /proc file, starting at the
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beginning.
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return value: the number of chars written to buf.
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This is all you have to do if all information fits in the buffer (it is
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about 3K in length). You can safely ignore offset and start in this case.
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If your /proc entry gets larger, you have to do a bit more work.
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(INPUT)
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buf: See above
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len: see above
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offset: The offset from the beginning of the /proc file where the user
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wants to start reading
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(OUTPUT)
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*buf: A part of the /proc file. The requested information does not
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have to start at the beginning.
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start: this is the place within buf where the information starts (ie.
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you must use offset to compute this!).
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return value: The number of valid characters written to buf. Begin
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counting at start, not at buf!
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You do not have to worry about not the whole information being in buf.
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Another call will be done (with a higher offset value) if more is
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needed.
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LINUX KERNEL 2.1.x, from 2.1.29 upwards
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=======================================
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This function is known as the read_proc function.
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int read_proc(char *buf, char **start, off_t offset, int len, int *eof,
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void *private);
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(INPUT)
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buf: A kernel-space buffer where we can put the information.
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len: The buffer length (we have a bit of slack here: if we write
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'a little' beyond this, things will still work out)
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(OUTPUT)
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*buf: The complete contents of the /proc file, starting at the
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beginning.
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eof: You can set this to true (anything but 0) to indicate we have
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reached the end of the file with this read. Not strictly
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necessary, but it is more efficient (else this function may be
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called again).
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return value: The number of valid characters written to buf. Begin
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counting at start, not at buf!
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If your /proc entry gets larger, you have to do a bit more work.
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(INPUT)
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buf: See above
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len: See above
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offset: The offset from the beginning of the /proc file where the user
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wants to start reading
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(OUTPUT)
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*buf: A part of the /proc file. The requested information does not
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have to start at the beginning.
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eof: See above
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start: this is the place within buf where the information starts (ie.
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you must use offset to compute this!).
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return value: The number of valid characters written to buf.
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You do not have to worry about not the whole information being in buf.
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Another call will be done (with a higher offset value) if more is
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needed. Ignore private.
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A third way to do this:
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(INPUT)
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buf: See above
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len: See above
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offset: The offset from the beginning of the /proc file where the user
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wants to start reading
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(OUTPUT)
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*buf: A part of the /proc file, with the requested information starting
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at the beginning.
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eof: See above
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start: (long)start is added to the offset pointer after reading. This
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allows you to play tricks with the file offset, independent of
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the number of read bytes.
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return value: the number of chars written to buf.
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This document was written by Frodo Looijaard <frodol@dds.nl>. I do not
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accept any responsibility for omissions or errors, but you are free to
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drop me a note if something is wrong or if you miss something.
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