linux-kernel - [RFC PATCH v1 3/3] vmcore: read vmcore through direct mapping region

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Date:	Thu, 10 Jan 2013 20:59:51 +0900
From:	HATAYAMA Daisuke <d.hatayama@...fujitsu.com>
To:	ebiederm@...ssion.com, vgoyal@...hat.com, cpw@....com,
	kumagai-atsushi@....nes.nec.co.jp, lisa.mitchell@...com
Cc:	kexec@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [RFC PATCH v1 3/3] vmcore: read vmcore through direct mapping region

Now regions represented by vmcore are mapped through direct mapping
region. We reads requested memory through direct mapping region
instead of using ioremap.

Notice that we still keep read_from_oldmem that uses ioremap because
we need to use it when reading elf headers to make vmcore_list in
vmcore initialization.

Signed-off-by: HATAYAMA Daisuke <d.hatayama@...fujitsu.com>
---

 fs/proc/vmcore.c |   45 ++++++++++++++++++++++++++++++++++++++++++++-
 1 files changed, 44 insertions(+), 1 deletions(-)

diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c
index aa14570..1c6259e 100644
--- a/fs/proc/vmcore.c
+++ b/fs/proc/vmcore.c
@@ -123,6 +123,49 @@ static ssize_t read_from_oldmem(char *buf, size_t count,
 	return read;
 }
 
+/* Reads a page from the oldmem device from given offset. */
+static ssize_t read_from_oldmem_noioremap(char *buf, size_t count,
+					  u64 *ppos, int userbuf)
+{
+        unsigned long pfn, offset;
+        size_t nr_bytes;
+        ssize_t read = 0;
+
+        if (!count)
+                return 0;
+
+        offset = (unsigned long)(*ppos % PAGE_SIZE);
+        pfn = (unsigned long)(*ppos / PAGE_SIZE);
+
+        do {
+                if (count > (PAGE_SIZE - offset))
+                        nr_bytes = PAGE_SIZE - offset;
+                else
+                        nr_bytes = count;
+
+                /* If pfn is not ram, return zeros for sparse dump files */
+                if (pfn_is_ram(pfn) == 0)
+                        memset(buf, 0, nr_bytes);
+                else {
+                        void *vaddr = pfn_to_kaddr(pfn);
+
+                        if (userbuf) {
+                                if (copy_to_user(buf, vaddr + offset, nr_bytes))
+                                        return -EFAULT;
+                        } else
+                                memcpy(buf, vaddr + offset, nr_bytes);
+                }
+                *ppos += nr_bytes;
+                count -= nr_bytes;
+                buf += nr_bytes;
+                read += nr_bytes;
+                ++pfn;
+                offset = 0;
+        } while (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)
@@ -553,7 +596,7 @@ static ssize_t read_vmcore(struct file *file, char __user *buffer,
 		tsz = nr_bytes;
 
 	while (buflen) {
-		tmp = read_from_oldmem(buffer, tsz, &start, 1);
+		tmp = read_from_oldmem_noioremap(buffer, tsz, &start, 1);
 		if (tmp < 0)
 			return tmp;
 		buflen -= tsz;

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