[PATCH 2/6][TAKE4] fallocate() on s390

["Amit K. Arora" <aarora@linux.vnet.ibm.com>]

This is the patch suggested by Martin Schwidefsky to support
sys_fallocate() on s390(x) platform.

He also suggested a wrapper in glibc to handle this system call on
s390. Posting it here so that we get feedback for this too.

.globl __fallocate
ENTRY(__fallocate)
	stm	%r6,%r7,28(%r15)	/* save %r6/%r7 on stack */
	cfi_offset (%r7, -68)
	cfi_offset (%r6, -72)
	lm	%r6,%r7,96(%r15)	/* load loff_t len from stack */
	svc	SYS_ify(fallocate)
	lm	%r6,%r7,28(%r15)	/* restore %r6/%r7 from stack */
	br	%r14
PSEUDO_END(__fallocate)


Here are the comments and the patch to linux kernel from him.

-------------
From: Martin Schwidefsky <schwidefsky@de.ibm.com>

This patch implements support of fallocate system call on s390(x)
platform. A wrapper is added to address the issue which s390 ABI has
with the arguments of this system call.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
---
 arch/s390/kernel/compat_wrapper.S |   10 ++++++++++
 arch/s390/kernel/sys_s390.c       |   29 +++++++++++++++++++++++++++++
 arch/s390/kernel/syscalls.S       |    1 +
 include/asm-s390/unistd.h         |    3 ++-
 4 files changed, 42 insertions(+), 1 deletion(-)

Index: linux-2.6.22-rc1/arch/s390/kernel/compat_wrapper.S
===================================================================
--- linux-2.6.22-rc1.orig/arch/s390/kernel/compat_wrapper.S
+++ linux-2.6.22-rc1/arch/s390/kernel/compat_wrapper.S
@@ -1682,3 +1682,13 @@ compat_sys_utimes_wrapper:
 	llgtr	%r2,%r2			# char *
 	llgtr	%r3,%r3			# struct compat_timeval *
 	jg	compat_sys_utimes
+
+	.globl  sys_fallocate_wrapper
+sys_fallocate_wrapper:
+	lgfr	%r2,%r2			# int
+	lgfr	%r3,%r3			# int
+	sllg    %r4,%r4,32		# get high word of 64bit loff_t
+	lr      %r4,%r5			# get low word of 64bit loff_t
+	sllg    %r5,%r6,32		# get high word of 64bit loff_t
+	l	%r5,164(%r15)		# get low word of 64bit loff_t
+	jg	sys_fallocate
Index: linux-2.6.22-rc1/arch/s390/kernel/sys_s390.c
===================================================================
--- linux-2.6.22-rc1.orig/arch/s390/kernel/sys_s390.c
+++ linux-2.6.22-rc1/arch/s390/kernel/sys_s390.c
@@ -265,3 +265,32 @@ s390_fadvise64_64(struct fadvise64_64_ar
 		return -EFAULT;
 	return sys_fadvise64_64(a.fd, a.offset, a.len, a.advice);
 }
+
+#ifndef CONFIG_64BIT
+/*
+ * This is a wrapper to call sys_fallocate(). For 31 bit s390 the last
+ * 64 bit argument "len" is split into the upper and lower 32 bits. The
+ * system call wrapper in the user space loads the value to %r6/%r7.
+ * The code in entry.S keeps the values in %r2 - %r6 where they are and
+ * stores %r7 to 96(%r15). But the standard C linkage requires that
+ * the whole 64 bit value for len is stored on the stack and doesn't
+ * use %r6 at all. So s390_fallocate has to convert the arguments from
+ *   %r2: fd, %r3: mode, %r4/%r5: offset, %r6/96(%r15)-99(%r15): len
+ * to
+ *   %r2: fd, %r3: mode, %r4/%r5: offset, 96(%r15)-103(%r15): len
+ */
+asmlinkage long s390_fallocate(int fd, int mode, loff_t offset,
+			       u32 len_high, u32 len_low)
+{
+	union {
+		u64 len;
+		struct {
+			u32 high;
+			u32 low;
+		};
+	} cv;
+	cv.high = len_high;
+	cv.low = len_low;
+	return sys_fallocate(fd, mode, offset, cv.len);
+}
+#endif
Index: linux-2.6.22-rc1/arch/s390/kernel/syscalls.S
===================================================================
--- linux-2.6.22-rc1.orig/arch/s390/kernel/syscalls.S
+++ linux-2.6.22-rc1/arch/s390/kernel/syscalls.S
@@ -322,3 +322,4 @@ NI_SYSCALL							/* 310 sys_move_pages *
 SYSCALL(sys_getcpu,sys_getcpu,sys_getcpu_wrapper)
 SYSCALL(sys_epoll_pwait,sys_epoll_pwait,compat_sys_epoll_pwait_wrapper)
 SYSCALL(sys_utimes,sys_utimes,compat_sys_utimes_wrapper)
+SYSCALL(s390_fallocate,sys_fallocate,sys_fallocate_wrapper)
Index: linux-2.6.22-rc1/include/asm-s390/unistd.h
===================================================================
--- linux-2.6.22-rc1.orig/include/asm-s390/unistd.h
+++ linux-2.6.22-rc1/include/asm-s390/unistd.h
@@ -251,8 +251,9 @@
 #define __NR_getcpu		311
 #define __NR_epoll_pwait	312
 #define __NR_utimes		313
+#define __NR_fallocate		314
 
-#define NR_syscalls 314
+#define NR_syscalls 315
 
 /* 
  * There are some system calls that are not present on 64 bit, some