Re: RFC: new utility, kmodpatch

Hi!

Do You think for this project: http://www.ksplice.com/ ?

On 1/1/09, Luigi Rizzo <rizzo_at_iet.unipi.it> wrote:
> I mentioned this utility a couple of months ago, and it's now working
> so i would like to receive feedback on whether this is good to have
> as part of the system, or just keep it as a port (which is what
> i plan to do by default).
>
> In a nutshell, the kmodpatch utility can print or alter the content
> of device/quirk tables in kernel modules (I think Linux has some
> similar tool, though i don't remember the name -- or perhaps it is
> a feature of insmod ?).
>
> Full manpage is attached at the end, full sources are at
>
>     http://info.iet.unipi.it/~luigi/FreeBSD/20090101-kmodpatch.tgz
>
> What is missing is some extra code to let it patch an on-disk file
> (elfdump returns the info we need, so in the worst case we just
> need to write a wrapper around elfdump).
>
> Feedback welcome.
>
> 	cheers
> 	luigi
>
> ------- manpage content --------
>
> KMODPATCH(8)            FreeBSD System Manager's Manual
> KMODPATCH(8)
>
> NAME
>      kmodpatch -- print/modify device/quirk tables in kernel modules
>
> SYNOPSIS
>      kmodpatch [-v] [-t file | format] module_name table_name [_at_offset [args
>                ...]]
>
> DESCRIPTION
>      The kmodpatch utility can print or alter the content of device/quirk
>      tables in kernel modules. These tables are generally used to identify
>      devices, and possibly apply specific quirks to enable/disable certain
>      features.  kmodpatch is especially useful to let the kernel recognise a
>      new device without rebooting and rebuilding/reinstalling kernel or mod-
>      ules.
>
>      In read mode (when no args are specified), kmodpatch only list one or
>      more entries in the matching module and table.
>
>      In write mode, kmodpatch overwrites a user's specified entry in a table
>      with the values passed on the command line.  kmodpatch does some amount
>      of checking to make sure that the arguments (module and table name,
> off-
>      set, parameters formats) are compatible with the currently loaded mod-
>      ules.
>
>      A couple of real life examples:
>
>      kmodpatch umass.ko - _at_0 0x4050 0x4a5 0x0101 0x4200
>          set the kernel to use flags UMASS_PROTO_SCSI | UMASS_PROTO_BBB and
>          quirks WRONG_CSWSIG | NO_SYNCHRONIZE_CACHE for a certain GSM phone
>          that implements the umass interface;
>
>      kmodpatch uscanner.ko - _at_0 0x04b8 0x084a 0
>          let uscanner.ko recognise a newly introduced MFP scanner device.
>
>      kmodpatch relies on a list of which modules and tables (associated to
>      kernel symbols) it can work on, and the format of the records in each
> ta-
>      ble.  By default kmodpatch uses an internal list, which can be
> overridden
>      from the command line using the -t option followed by either a file
> name,
>      or by immediate text describing the kernel table.  The format of the
> file
>      is described in Section MODULE DESCRIPTION
>
>      The following options are available:
>
>      -v      Verbose mode, print some debugging info
>
>      -t file | format
>              Specify a file containing the name and format of descriptor
>              tables, or a line with the actual format of the table.
>
> MODULE DESCRIPTION
>      The file (or text) describing modules, tables and record structure has
> a
>      simple text format with one line per table. The `#' character is a com-
>      ment delimiter, and can appear anywhere in the text.  Each valid line
>      must contain the following fields:
>
>      module_name symbol_name entry_format [entry_format ...]
>
>      Each entry_format describes one field in the table, and it is made of a
>      number and/or a character specifying the field size and format,
> followed
>      by an optional ':' and a word describing the field itself.
>
>      Supported formats are:
>
>      2 | 2l | 2b
>              16-bit unsigned in host, little-endian or big-endian format;
>
>      4 | 4l | 4b
>              32-bit unsigned in host, little-endian or big-endian format;
>
>      8 | 8l | 8b
>              64-bit unsigned in host, little-endian or big-endian format;
>
>      p       a pointer;
>
>      s       a null-terminated string;
>
>      The optional description is used as a header when listing the content
> of
>      a table.
>
>    EXAMPLE MODULE DESCRIPTION
>      The following is an example of a file containing module descriptions.
>
>            umass.ko    umass_devdescrs 4:vendor 4:product 4:rev 2:proto
> 2:quirks
>            uscanner.ko uscanner_devs   2:vendor 2:device 4:flags # comment
>            if_nfe.ko   nfe_devs        2:vendor 2:device s:name
>            if_re.ko    re_devs         2:vendor 2:device 4:type s:name
>
> EXAMPLES
>      In addition to the two examples given at the beginning, one can use
>      kmodpatch to explore the content of kernel tables, as follows.
>
>      To list entries in module if_re:
>
>            kmodpatch if_re -
>
>      To list entry 10 in module umass:
>
>            kmodpatch umass - _at_10
>
>      To set the last entry in module uscanner.ko
>
>            kmodpatch uscanner.ko - _at_-1 0x04b8 0x0839 0
>
> WARNINGS
>      kmodpatch requires root privileges even to just read the content of the
>      kernel tables.
>
>      In write mode, the use of kmodpatch is as dangerous as accessing
>      /dev/kmem in write mode, even though kmodpatch does some amount of
> check-
>      ing to make sure that the arguments passed are reasonable. To this pur-
>      pose, it is fundamental that the table descriptions used by kmodpatch
>      match the actual structure of the kernel tables.  There is no automatic
>      way to extract this info.
>
> BUGS
>      Right now, kmodpatch only writes to in-memory modules (or kernel). As a
>      consequence the approach is not suitable to devices that are
> persistently
>      connected to the system and for which the system cannot do a "reprobe".
>
> SEE ALSO
>      kldconfig(8), kldload(8), kldstat(8), kldunload(8)
>
> HISTORY
>      The kmodpatch utility first appeared in FreeBSD 8.0 inspired by a
> similar
>      feature present on Linux.
>
> AUTHORS
>      The kmodpatch utility was designed and implemented by Luigi Rizzo
>      <luigi_at_FreeBSD.org>.
>
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