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Subject[PATCH v3 0/3] resource: Use list_head to link sibling resource
Date
This patchset mainly converts strut resource's sibling list from singly
linked list to doubly linked list, list_head. This is suggested by
Andrew. Since I need a reversed searching on iomem_resource's
IORESOURCE_SYSTEM_RAM children, the old singly linked list way makes
the code in v1 post really ugly.

With this change, we only need one simple list_for_each_entry_reverse()
to do reversed iteration on sibling list. The relevant codes in
kernel/resource.c are more readable since those dazzling pointer
operation codes for singly linked list are replaced.

With the help of list_head, in patch 0002 we can have a very simple
walk_system_ram_res_rev(). And in patch 0003, will use it to search
available system RAM region for kexec_buffer of kexec_file from top to
down, just like we have been doing all along in kexec loading which is
done in kexec-tools utility.

Note:
This patchset passed testing on my kvm guest, x86_64 arch with network
enabling. The thing we need pay attetion to is that a root resource's
child member need be initialized specifically with LIST_HEAD_INIT() if
sttically defined or INIT_LIST_HEAD() for dynamically definition. Here
Just like we do for iomem_resource/ioport_resource, or the change in
get_pci_domain_busn_res().

And there are two places of change I am not very sure. One is in
drivers/hv/vmbus_drv.c, the other is in drivers/pci/host/vmd.c. So will
invite experts on these areas to help review.

V2 post and discussions can be found here:
https://lkml.org/lkml/2018/4/7/169

Remaining issue:
Rob raised issue that if we can make an common tree struct and helpers
defined on top of list_head or a new struct, quote his saying as below.
I didn't do much investigation, we may have a new struct like

struct tlist {
void *parent;
struct list_head sibling;
struct list_head child;
}

Since I have some rhel dev things right now, may consider this later, put
it in my TODO list. In kernel, like task_struct, task_group, they all have
this kind of tree list, and have used list_head. If anyone is interested,
feel free to have a try on this.

==========
The DT struct device_node also has the same tree structure with
parent, child, sibling pointers and converting to list_head had been
on the todo list for a while. ACPI also has some tree walking
functions (drivers/acpi/acpica/pstree.c). Perhaps there should be a
common tree struct and helpers defined either on top of list_head or a
new struct if that saves some size.
==========


Changelog:
v2->v3:
Rename resource functions first_child() and sibling() to
resource_first_chils() and resource_sibling(). Dan suggested this.

Move resource_first_chils() and resource_sibling() to linux/ioport.h
and make them as inline function. Rob suggested this. Accordingly add
linux/list.h including in linux/ioport.h, please help review if this
bring efficiency degradation or code redundancy.

The change on struct resource {} bring two pointers of size increase,
mention this in git log to make it more specifically, Rob suggested
this.

v1->v2:
Use list_head instead to link resource siblings. This is suggested by
Andrew.

Rewrite walk_system_ram_res_rev() after list_head is taken to link
resouce siblings.

Baoquan He (3):
resource: Use list_head to link sibling resource
resource: add walk_system_ram_res_rev()
kexec_file: Load kernel at top of system RAM if required

arch/sparc/kernel/ioport.c | 2 +-
drivers/gpu/drm/drm_memory.c | 3 +-
drivers/gpu/drm/gma500/gtt.c | 5 +-
drivers/hv/vmbus_drv.c | 52 +++----
drivers/input/joystick/iforce/iforce-main.c | 4 +-
drivers/nvdimm/e820.c | 2 +-
drivers/nvdimm/namespace_devs.c | 6 +-
drivers/nvdimm/nd.h | 5 +-
drivers/of/address.c | 4 +-
drivers/parisc/lba_pci.c | 4 +-
drivers/pci/host/vmd.c | 8 +-
drivers/pci/probe.c | 2 +
drivers/pci/setup-bus.c | 2 +-
include/linux/ioport.h | 20 ++-
kernel/kexec_file.c | 2 +
kernel/resource.c | 221 ++++++++++++++++------------
16 files changed, 193 insertions(+), 149 deletions(-)

--
2.13.6

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