crash/0028-memory-zram-introduce-and-export-readswap.patch

From 74474a366d1244d344ad9ff222e8e2351a96af8c Mon Sep 17 00:00:00 2001
From: HATAYAMA Daisuke <d.hatayama@fujitsu.com>
Date: Fri, 25 Dec 2020 15:48:50 +0900
Subject: [PATCH 09/11] memory, zram: introduce and export readswap()

try_zram_decompress() is currently exported to extension modules, but
from a viewpoint of author of extension modules, it's better to export
an interface to read memory on swap; difference of decompressor are
then hidden within the interface and there is no need for extension
modules to update accordingly each time new decompressor are added in
the future.

So let's introduce function readswap() as an interface to read memory
on swap.

Signed-off-by: HATAYAMA Daisuke <d.hatayama@fujitsu.com>
---
 defs.h     |  1 +
 diskdump.c | 63 ++++++++++++++++++++++++++++++++++++++----------------
 memory.c   |  2 +-
 3 files changed, 46 insertions(+), 20 deletions(-)

diff --git a/defs.h b/defs.h
index ebd7bb615b61..c29b3fa3dee9 100644
--- a/defs.h
+++ b/defs.h
@@ -6539,6 +6539,7 @@ int diskdump_get_nr_cpus(void);
 QEMUCPUState *diskdump_get_qemucpustate(int);
 void diskdump_device_dump_info(FILE *);
 void diskdump_device_dump_extract(int, char *, FILE *);
+ulong readswap(ulonglong pte_val, char *buf, ulong len, ulonglong vaddr);
 /*support for zram*/
 ulong try_zram_decompress(ulonglong pte_val, unsigned char *buf, ulong len, ulonglong vaddr);
 #define OBJ_TAG_BITS     1
diff --git a/diskdump.c b/diskdump.c
index a4ca38f6c732..03a77a977646 100644
--- a/diskdump.c
+++ b/diskdump.c
@@ -2709,24 +2709,13 @@ lookup_swap_cache(ulonglong pte_val, unsigned char *zram_buf)
 	return NULL;
 }
 
-ulong (*decompressor)(unsigned char *in_addr, ulong in_size, unsigned char *out_addr, ulong *out_size, void *other/* NOT USED */);
-/*
- * If userspace address was swapped out to zram, this function is called to decompress the object.
- * try_zram_decompress returns decompressed page data and data length
- */
-ulong 
-try_zram_decompress(ulonglong pte_val, unsigned char *buf, ulong len, ulonglong vaddr)
+static int get_disk_name_private_data(ulonglong pte_val, ulonglong vaddr,
+				       char *name, ulong *private_data)
 {
-	char name[32] = {0};
-	ulonglong swp_offset;
-	ulong swap_info, bdev, bd_disk, zram, zram_table_entry, sector, index, entry, flags, size, outsize, off;
-	unsigned char *obj_addr = NULL;
-	unsigned char *zram_buf = NULL;
-	unsigned char *outbuf = NULL;
+	ulong swap_info, bdev, bd_disk;
 
-	off = PAGEOFFSET(vaddr);
 	if (!symbol_exists("swap_info"))
-		return 0;
+		return FALSE;
 
 	swap_info = symbol_value("swap_info");
 
@@ -2743,14 +2732,49 @@ try_zram_decompress(ulonglong pte_val, unsigned char *buf, ulong len, ulonglong
 			sizeof(void *), "swap_info_struct_bdev", FAULT_ON_ERROR);
 	readmem(bdev + OFFSET(block_device_bd_disk), KVADDR, &bd_disk,
 			sizeof(void *), "block_device_bd_disk", FAULT_ON_ERROR);
-	readmem(bd_disk + OFFSET(gendisk_disk_name), KVADDR, name,
+	if (name)
+		readmem(bd_disk + OFFSET(gendisk_disk_name), KVADDR, name,
 			strlen("zram"), "gendisk_disk_name", FAULT_ON_ERROR);
+	if (private_data)
+		readmem(bd_disk + OFFSET(gendisk_private_data), KVADDR,
+			private_data, sizeof(void *), "gendisk_private_data",
+			FAULT_ON_ERROR);
+
+	return TRUE;
+}
+
+ulong readswap(ulonglong pte_val, char *buf, ulong len, ulonglong vaddr)
+{
+	char name[32] = {0};
 
-	if (strncmp(name, "zram", strlen("zram"))) {
+	if (!get_disk_name_private_data(pte_val, vaddr, name, NULL))
+		return 0;
+
+	if (!strncmp(name, "zram", 4)) {
+		return try_zram_decompress(pte_val, (unsigned char *)buf, len, vaddr);
+	} else {
 		if (CRASHDEBUG(2))
 			error(WARNING, "this page has been swapped to %s\n", name);
 		return 0;
 	}
+}
+
+ulong (*decompressor)(unsigned char *in_addr, ulong in_size, unsigned char *out_addr,
+			ulong *out_size, void *other/* NOT USED */);
+/*
+ * If userspace address was swapped out to zram, this function is called to decompress the object.
+ * try_zram_decompress returns decompressed page data and data length
+ */
+ulong
+try_zram_decompress(ulonglong pte_val, unsigned char *buf, ulong len, ulonglong vaddr)
+{
+	char name[32] = {0};
+	ulonglong swp_offset;
+	unsigned char *obj_addr = NULL;
+	unsigned char *zram_buf = NULL;
+	unsigned char *outbuf = NULL;
+	ulong zram, zram_table_entry, sector, index, entry, flags, size,
+		outsize, off;
 
 	if (INVALID_MEMBER(zram_compressor)) {
 		zram_init();
@@ -2765,8 +2789,8 @@ try_zram_decompress(ulonglong pte_val, unsigned char *buf, ulong len, ulonglong
 	if (CRASHDEBUG(2))
 		error(WARNING, "this page has swapped to zram\n");
 
-	readmem(bd_disk + OFFSET(gendisk_private_data), KVADDR, &zram,
-		sizeof(void *), "gendisk_private_data", FAULT_ON_ERROR);
+	if (!get_disk_name_private_data(pte_val, vaddr, NULL, &zram))
+		return 0;
 
 	readmem(zram + OFFSET(zram_compressor), KVADDR, name,
 		sizeof(name), "zram compressor", FAULT_ON_ERROR);
@@ -2798,6 +2822,7 @@ try_zram_decompress(ulonglong pte_val, unsigned char *buf, ulong len, ulonglong
 
 	zram_buf = (unsigned char *)GETBUF(PAGESIZE());
 	/* lookup page from swap cache */
+	off = PAGEOFFSET(vaddr);
 	obj_addr = lookup_swap_cache(pte_val, zram_buf);
 	if (obj_addr != NULL) {
 		memcpy(buf, obj_addr + off, len);
diff --git a/memory.c b/memory.c
index 33b0ca7af977..17ac40b3e0f9 100644
--- a/memory.c
+++ b/memory.c
@@ -2294,7 +2294,7 @@ readmem(ulonglong addr, int memtype, void *buffer, long size,
 					if (cnt > size)
 						cnt = size;
 
-					cnt = try_zram_decompress(paddr, (unsigned char *)bufptr, cnt, addr);
+					cnt = readswap(paddr, bufptr, cnt, addr);
 					if (cnt) {
 						bufptr += cnt;
 						addr += cnt;
-- 
2.29.2