[RHEL6.8 Patch 06/19] vmcore: clean up read_vmcore()

[Baoquan He <bhe@redhat.com>]

Resolves: bz1097904
https://bugzilla.redhat.com/show_bug.cgi?id=1097904

This is back ported from upstream directly.

commit b27eb186608c89ef0979ae47c649859ceaa1b2e7
Author: HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com>
Date:   Wed Jul 3 15:02:13 2013 -0700

    vmcore: clean up read_vmcore()

    Rewrite part of read_vmcore() that reads objects in vmcore_list in the
    same way as part reading ELF headers, by which some duplicated and
    redundant codes are removed.

    Signed-off-by: HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com>
    Acked-by: Vivek Goyal <vgoyal@redhat.com>
    Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
    Cc: Atsushi Kumagai <kumagai-atsushi@mxc.nes.nec.co.jp>
    Cc: Lisa Mitchell <lisa.mitchell@hp.com>
    Cc: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Signed-off-by: Baoquan He <bhe@redhat.com>
---
 fs/proc/vmcore.c | 68 +++++++++++++++++---------------------------------------
 1 file changed, 20 insertions(+), 48 deletions(-)

diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c
index 1def40a..861956c 100644
--- a/fs/proc/vmcore.c
+++ b/fs/proc/vmcore.c
@@ -114,27 +114,6 @@ static ssize_t read_from_oldmem(char *buf, size_t count,
 	return read;
 }
 
-/* Maps vmcore file offset to respective physical address in memroy. */
-static u64 map_offset_to_paddr(loff_t offset, struct list_head *vc_list,
-					struct vmcore **m_ptr)
-{
-	struct vmcore *m;
-	u64 paddr;
-
-	list_for_each_entry(m, vc_list, list) {
-		u64 start, end;
-		start = m->offset;
-		end = m->offset + m->size - 1;
-		if (offset >= start && offset <= end) {
-			paddr = m->paddr + offset - start;
-			*m_ptr = m;
-			return paddr;
-		}
-	}
-	*m_ptr = NULL;
-	return 0;
-}
-
 /* Read from the ELF header and then the crash dump. On error, negative value is
  * returned otherwise number of bytes read are returned.
  */
@@ -143,8 +122,8 @@ static ssize_t read_vmcore(struct file *file, char __user *buffer,
 {
 	ssize_t acc = 0, tmp;
 	size_t tsz;
-	u64 start, nr_bytes;
-	struct vmcore *curr_m = NULL;
+	u64 start;
+	struct vmcore *m = NULL;
 
 	if (buflen == 0 || *fpos >= vmcore_size)
 		return 0;
@@ -170,33 +149,26 @@ static ssize_t read_vmcore(struct file *file, char __user *buffer,
 			return acc;
 	}
 
-	start = map_offset_to_paddr(*fpos, &vmcore_list, &curr_m);
-	if (!curr_m)
-        	return -EINVAL;
-
-	while (buflen) {
-		tsz = min_t(size_t, buflen, PAGE_SIZE - (start & ~PAGE_MASK));
-
-		/* Calculate left bytes in current memory segment. */
-		nr_bytes = (curr_m->size - (start - curr_m->paddr));
-		if (tsz > nr_bytes)
-			tsz = nr_bytes;
-
-		tmp = read_from_oldmem(buffer, tsz, &start, 1);
-		if (tmp < 0)
-			return tmp;
-		buflen -= tsz;
-		*fpos += tsz;
-		buffer += tsz;
-		acc += tsz;
-		if (start >= (curr_m->paddr + curr_m->size)) {
-			if (curr_m->list.next == &vmcore_list)
-				return acc;	/*EOF*/
-			curr_m = list_entry(curr_m->list.next,
-						struct vmcore, list);
-			start = curr_m->paddr;
+	list_for_each_entry(m, &vmcore_list, list) {
+		if (*fpos < m->offset + m->size) {
+			tsz = m->offset + m->size - *fpos;
+			if (buflen < tsz)
+				tsz = buflen;
+			start = m->paddr + *fpos - m->offset;
+			tmp = read_from_oldmem(buffer, tsz, &start, 1);
+			if (tmp < 0)
+				return tmp;
+			buflen -= tsz;
+			*fpos += tsz;
+			buffer += tsz;
+			acc += tsz;
+
+			/* leave now if filled buffer already */
+			if (buflen == 0)
+				return acc;
 		}
 	}
+
 	return acc;
 }
 
-- 
2.1.0