[PATCH v2] ACPI: Add sysfs links from memory device to memblocks

[Toshi Kani]

In order to eject a memory device object represented as "PNP0C80:%d"
in sysfs, its associated memblocks (system/memory/memory%d) need to
be off-lined.  However, there is no user friendly way to correlate
between a memory device object and its memblocks in sysfs.

This patch creates sysfs links to memblocks under a memory device
object so that a user can easily checks and manipulates its memblocks
in sysfs.

For example, when PNP0C80:05 is associated with memory8 and memory9,
the following two links are created under PNP0C80:05.  This allows
a user to access memory8/9 directly from PNP0C80:05.

  # ll /sys/devices/LNXSYSTM:00/LNXSYBUS:00/PNP0C80:05
  lrwxrwxrwx. memory8 -> ../../../system/memory/memory8
  lrwxrwxrwx. memory9 -> ../../../system/memory/memory9

Signed-off-by: Toshi Kani <toshi.kani@xxxxxx>
---

This patch applies on top of the Rafael's patch below.
https://patchwork.kernel.org/patch/2153261/

v2: Added a NULL return check for find_memory_block_hinted() as
pointed by Yasuaki Ishimatsu.

---
 drivers/acpi/acpi_memhotplug.c |   56 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 56 insertions(+)

diff --git a/drivers/acpi/acpi_memhotplug.c b/drivers/acpi/acpi_memhotplug.c
index 3b3abbc..98477a5 100644
--- a/drivers/acpi/acpi_memhotplug.c
+++ b/drivers/acpi/acpi_memhotplug.c
@@ -28,6 +28,7 @@
  */
 
 #include <linux/acpi.h>
+#include <linux/memory.h>
 #include <linux/memory_hotplug.h>
 
 #include "internal.h"
@@ -168,6 +169,55 @@ static int acpi_memory_check_device(struct acpi_memory_device *mem_device)
 	return 0;
 }
 
+static void acpi_setup_mem_blk_links(struct acpi_memory_device *mem_device,
+		struct acpi_memory_info *info, bool add_links)
+{
+	struct memory_block *mem_blk = NULL;
+	struct mem_section *mem_sect;
+	unsigned long start_pfn, end_pfn, pfn;
+	unsigned long section_nr;
+	int ret;
+
+	start_pfn = PFN_DOWN(info->start_addr);
+	end_pfn = PFN_UP(info->start_addr + info->length-1);
+
+	for (pfn = start_pfn; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
+		section_nr = pfn_to_section_nr(pfn);
+
+		if (!present_section_nr(section_nr))
+			continue;
+
+		mem_sect = __nr_to_section(section_nr);
+
+		/* skip if the same memblock */
+		if (mem_blk)
+			if ((section_nr >= mem_blk->start_section_nr) &&
+			    (section_nr <= mem_blk->end_section_nr))
+				continue;
+
+		mem_blk = find_memory_block_hinted(mem_sect, mem_blk);
+		if (!mem_blk)
+			continue;
+
+		if (add_links) {
+			ret = sysfs_create_link_nowarn(
+				&mem_device->device->dev.kobj,
+				&mem_blk->dev.kobj,
+				kobject_name(&mem_blk->dev.kobj));
+			if (ret && ret != -EEXIST)
+				dev_err(&mem_device->device->dev,
+					"Failed to create sysfs link %s\n",
+					kobject_name(&mem_blk->dev.kobj));
+		} else {
+			sysfs_remove_link(&mem_device->device->dev.kobj,
+				kobject_name(&mem_blk->dev.kobj));
+		}
+	}
+
+	if (mem_blk)
+		kobject_put(&mem_blk->dev.kobj);
+}
+
 static int acpi_memory_enable_device(struct acpi_memory_device *mem_device)
 {
 	int result, num_enabled = 0;
@@ -207,6 +257,9 @@ static int acpi_memory_enable_device(struct acpi_memory_device *mem_device)
 			continue;
 		}
 
+		/* Create sysfs links to its mem_blk devices */
+		acpi_setup_mem_blk_links(mem_device, info, true);
+
 		if (!result)
 			info->enabled = 1;
 		/*
@@ -241,6 +294,9 @@ static int acpi_memory_remove_memory(struct acpi_memory_device *mem_device)
 			/* The kernel does not use this memory block */
 			continue;
 
+		/* Remove sysfs links to its mem_blk devices */
+		acpi_setup_mem_blk_links(mem_device, info, false);
+
 		if (!info->enabled)
 			/*
 			 * The kernel uses this memory block, but it may be not
--
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