Our apologies for the late notice, but RedHat has a set of
patches that apply to a xen-3.1.0 tarball to yield a set
of functioning pv-on-hvm drivers for RHEL3-U8 (& U9).
[A reduced set of patches would yield the same result w/3.1.2 .]
Our plans are to provide those patches to xen-devel in January,
after further cleanup (so they don't break 2.6 builds).
The patches have some similarities & differences to those listed
below. More specifically, they have what is described in 4, 5, & 6
(although I haven't had the time to compare the two implementations, but
a wheel typically comes out round ;-) ).
The patches differ in that h-file diffs are handled in the compat-include
directory. Additionally, the block device support is handled by a new
set of
interfaces, reducing potential issues of modifying this code for
Linux 2.4 breaking Linux 2.6, or vice versa.
The patches don't include a build system as described below, which
sounds like a clean way to handle those diffs, and avoid 2.4 vs 2.6
changes/diffs
over time (much like our separate block interface support split for 2.4
avoids conflicts/issues w/2.6).
The heavy lifting for this support was done by Herbert Xu.
I've been adding bug fixes and getting it into a clean set of patches
that can create an rpm that can be added to a rhel3 kernel,
as well as working with a number of testers asking for this support on
rhel3.
We'll look at the following patches in detail after the New Year.
(We turn into a pumpkin next week, and the fairy tale ends 1/2/08),
and see what we can meld into a patch set that takes the best
of both worlds.
- Don
===========================================================
Ben Guthro wrote:
This patch enables front end drivers to build under Linux 2.4.
Specifically, the 2.4.21-47 kernel is used. This corresponds to
RedHat Linux 3 update 8
release.
Changes were made in two areas. Files were changed in the unmodified
tree as
well as the sparse tree. The latter corresponds to the drivers/xen
tree in
the Linux 2.6.18 kernel and will be referred to as the "Linux driver
tree" in
the remainder of this note.
In the unmodified tree, changes were related to build system
modifications,
addition of missing header files, implementation of the generic
device model
code for kernel 2.4 and all other nuggets required to compile front
end drivers
under kernel 2.4.
In the Linux driver tree, changes made were located almost entirely
in the front
end drivers area. Most of these were related to implementation of
compatibility
macros and replacement of APIs which evolved, were added or removed
between
kernels 2.4 and 2.6. Where a one to one replacement of a specific
call was not
possible, blocks of code surrounded by kernel version specific
preprocessor
directives were added. One instance of this is disk geometry
processing.
Below is a more detailed list of changes made in the unmodified tree.
1. Build system. For each Kbuild file in the front driver area, a
corresponding K24build file has been created. There, 2.4 style
targets are
used. The main Makefile for each driver references appropriate "K"
file
depending on the kernel version the driver is being built for.
2. Nonexistent header files. Header files included in front end
drivers which
do not exist under kernel 2.4 were replaced by dummy headers.
These, in
turn, include compatibility headers to further resolve differences
between
kernel 2.4 and 2.6. Dummy header files reside in the
compat-include/linux
tree.
3. Block interface. Changed APIs are handled through compatibility
macros whose
names are usually of the form compat_<original function name>(). This
applies to:
a. end request processing; Note that some of these macros take the
same
number of arguments as original 2.6 APIs. The change of name is
necessary
because, while the corresponding 2.4 API exists, the number or
type of
arguments might have changed. This is the case for
end_that_request_first(), for example. Additionally, as also
happens to
be the case with this particular API, the way in which some APIs
are
called varies between kernels 2.4 and 2.6. Specifically, under
kernel
2.6, end_that_request_first() is called once with a pointer to
the request
being currently processed. The rest is done by the kernel.
However,
under kernel 2.4, this API is called repeatedly until a certain
return
code is obtained (which signals that the kernel is done with the
current
request). This difference of having to call it once (2.6) or,
potentially, many times (2.4) is covered in the corresponding
compatibility macro.
b. geometry calculations
c. references to bio and bio_vec structures are now translated into
references to buffer_head structures
d. resolution of driver's private data area pointer (struct
blkfront_info
pointer)
e. resolution of the generic disk pointer
4. Work queue interface. This is now implemented using scheduler
task queue.
5. Kernel thread interface. Those interfaces which are not defined
under kernel
2.4 are implemented in the compatibility header file using 2.4
versions of
thread functions.
6. Generic device model. A simplified version of device model
interfaces was
implemented to allow front end drivers to compile under kernel
2.4. All
required structures appear in the compatibility header file. All 2.4
versions of device model interfaces are implemented in
platform-compat.c in
platform-pci.o driver.
This list details changes made in the Linux driver tree.
1. Generic kernel compatibility header file. Instead of including
xen/platform-compat.h which is compiled in only conditionally, a
generic
compatibility header is included. This file, named kerncompat.h is
included
unconditionally and contains all compatibility macros used in front
end
drivers. Moreover, kerncompat.h conditionally includes
platform-compat.h
just as it was done in the original front end driver code.
Unconditional
usage of kerncompat.h is necessary to give front end drivers access to
compatibility macros.
2. Disk driver initialization and setup. Blocks of code needed to
handle
generic disk operation were added and are compiled for kernels
below 2.6.0.
3. Partition processing. Blocks of code needed to process partition
table
updates and geometry inquires were added. These are conditionally
compiled
for kernels below 2.6.0 only.
Signed-off-by: Paul Burkacki <pburkacki@xxxxxxxxxxxxxxx>
Signed-off-by: Ben Guthro <bguthro@xxxxxxxxxxxxxxx>
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