[PATCH 2/5][TAKE3] fallocate() on s390

Amit K. Arora
2007-05-15T20:10:42Z

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