linux-kernel - [PATCH 05/13] kexec: Make kexec_segment user buffer pointer a union

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Message-Id: <1401800822-27425-6-git-send-email-vgoyal@redhat.com>
Date:	Tue,  3 Jun 2014 09:06:54 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	linux-kernel@...r.kernel.org, kexec@...ts.infradead.org
Cc:	ebiederm@...ssion.com, hpa@...or.com, mjg59@...f.ucam.org,
	greg@...ah.com, bp@...en8.de, jkosina@...e.cz, dyoung@...hat.com,
	chaowang@...hat.com, bhe@...hat.com, akpm@...ux-foundation.org,
	Vivek Goyal <vgoyal@...hat.com>
Subject: [PATCH 05/13] kexec: Make kexec_segment user buffer pointer a union

So far kexec_segment->buf was always a user space pointer as user space
passed the array of kexec_segment structures and kernel copied it.

But with new system call, list of kexec segments will be prepared by
kernel and kexec_segment->buf will point to a kernel memory.

So while I was adding code where I made assumption that ->buf is pointing
to kernel memory, sparse started giving warning.

Make ->buf a union. And where a user space pointer is expected, access
it using ->buf and where a kernel space pointer is expected, access it
using ->kbuf. That takes care of sparse warnings.

Signed-off-by: Vivek Goyal <vgoyal@...hat.com>
---
 include/linux/kexec.h | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index a756419..d0285cc 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -69,7 +69,18 @@ typedef unsigned long kimage_entry_t;
 #define IND_SOURCE       0x8
 
 struct kexec_segment {
-	void __user *buf;
+	/*
+	 * This pointer can point to user memory if kexec_load() system
+	 * call is used or will point to kernel memory if
+	 * kexec_file_load() system call is used.
+	 *
+	 * Use ->buf when expecting to deal with user memory and use ->kbuf
+	 * when expecting to deal with kernel memory.
+	 */
+	union {
+		void __user *buf;
+		void *kbuf;
+	};
 	size_t bufsz;
 	unsigned long mem;
 	size_t memsz;
-- 
1.9.0

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