preadv/pwritev: Add preadv and pwritev system calls.

This patch adds preadv and pwritev system calls.  These syscalls are a
pretty straightforward combination of pread and readv (same for write).
They are quite useful for doing vectored I/O in threaded applications.
Using lseek+readv instead opens race windows you'll have to plug with
locking.

Other systems have such system calls too, for example NetBSD, check
here: http://www.daemon-systems.org/man/preadv.2.html

The application-visible interface provided by glibc should look like
this to be compatible to the existing implementations in the *BSD family:

  ssize_t preadv(int d, const struct iovec *iov, int iovcnt, off_t offset);
  ssize_t pwritev(int d, const struct iovec *iov, int iovcnt, off_t offset);

This prototype has one problem though: On 32bit archs is the (64bit)
offset argument unaligned, which the syscall ABI of several archs doesn't
allow to do.  At least s390 needs a wrapper in glibc to handle this.  As
we'll need a wrappers in glibc anyway I've decided to push problem to
glibc entriely and use a syscall prototype which works without
arch-specific wrappers inside the kernel: The offset argument is
explicitly splitted into two 32bit values.

The patch sports the actual system call implementation and the windup in
the x86 system call tables.  Other archs follow as separate patches.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: <linux-api@vger.kernel.org>
Cc: <linux-arch@vger.kernel.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

8 files changed, 106 insertions, 0 deletions

diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S
index db0c803170ab..a505202086e8 100644
--- a/arch/x86/ia32/ia32entry.S
+++ b/arch/x86/ia32/ia32entry.S
@@ -828,4 +828,6 @@ ia32_sys_call_table:
         .quad sys_dup3                  /* 330 */
         .quad sys_pipe2
         .quad sys_inotify_init1
+        .quad compat_sys_preadv
+        .quad compat_sys_pwritev
 ia32_syscall_end:
diff --git a/arch/x86/include/asm/unistd_32.h b/arch/x86/include/asm/unistd_32.h
index f2bba78430a4..6e72d74cf8dc 100644
--- a/arch/x86/include/asm/unistd_32.h
+++ b/arch/x86/include/asm/unistd_32.h
@@ -338,6 +338,8 @@
 #define __NR_dup3               330
 #define __NR_pipe2              331
 #define __NR_inotify_init1      332
+#define __NR_preadv             333
+#define __NR_pwritev            334
 
 #ifdef __KERNEL__
 
diff --git a/arch/x86/include/asm/unistd_64.h b/arch/x86/include/asm/unistd_64.h
index d2e415e6666f..f81829462325 100644
--- a/arch/x86/include/asm/unistd_64.h
+++ b/arch/x86/include/asm/unistd_64.h
@@ -653,6 +653,10 @@ __SYSCALL(__NR_dup3, sys_dup3)
 __SYSCALL(__NR_pipe2, sys_pipe2)
 #define __NR_inotify_init1                      294
 __SYSCALL(__NR_inotify_init1, sys_inotify_init1)
+#define __NR_preadv                             295
+__SYSCALL(__NR_preadv, sys_preadv)
+#define __NR_pwritev                            296
+__SYSCALL(__NR_pwritev, sys_pwritev)
 
 
 #ifndef __NO_STUBS
diff --git a/arch/x86/kernel/syscall_table_32.S b/arch/x86/kernel/syscall_table_32.S
index 3bdb64829b82..ff5c8736b491 100644
--- a/arch/x86/kernel/syscall_table_32.S
+++ b/arch/x86/kernel/syscall_table_32.S
@@ -332,3 +332,5 @@ ENTRY(sys_call_table)
         .long sys_dup3                  /* 330 */
         .long sys_pipe2
         .long sys_inotify_init1
+        .long sys_preadv
+        .long sys_pwritev
diff --git a/fs/compat.c b/fs/compat.c
index e04b4660db84..7c1615183d1e 100644
--- a/fs/compat.c
+++ b/fs/compat.c
@@ -1232,6 +1232,24 @@ compat_sys_readv(unsigned long fd, const struct compat_iovec __user *vec,
         return ret;
 }
 
+asmlinkage ssize_t
+compat_sys_preadv(unsigned long fd, const struct compat_iovec __user *vec,
+                  unsigned long vlen, u32 pos_high, u32 pos_low)
+{
+        loff_t pos = ((loff_t)pos_high << 32) | pos_low;
+        struct file *file;
+        ssize_t ret;
+
+        if (pos < 0)
+                return -EINVAL;
+        file = fget(fd);
+        if (!file)
+                return -EBADF;
+        ret = compat_readv(file, vec, vlen, &pos);
+        fput(file);
+        return ret;
+}
+
 static size_t compat_writev(struct file *file,
                             const struct compat_iovec __user *vec,
                             unsigned long vlen, loff_t *pos)
@@ -1269,6 +1287,24 @@ compat_sys_writev(unsigned long fd, const struct compat_iovec __user *vec,
         return ret;
 }
 
+asmlinkage ssize_t
+compat_sys_pwritev(unsigned long fd, const struct compat_iovec __user *vec,
+                   unsigned long vlen, u32 pos_high, u32 pos_low)
+{
+        loff_t pos = ((loff_t)pos_high << 32) | pos_low;
+        struct file *file;
+        ssize_t ret;
+
+        if (pos < 0)
+                return -EINVAL;
+        file = fget(fd);
+        if (!file)
+                return -EBADF;
+        ret = compat_writev(file, vec, vlen, &pos);
+        fput(file);
+        return ret;
+}
+
 asmlinkage long
 compat_sys_vmsplice(int fd, const struct compat_iovec __user *iov32,
                     unsigned int nr_segs, unsigned int flags)
diff --git a/fs/read_write.c b/fs/read_write.c
index 400fe81c973e..6d5d8ff238aa 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -731,6 +731,56 @@ SYSCALL_DEFINE3(writev, unsigned long, fd, const struct iovec __user *, vec,
         return ret;
 }
 
+SYSCALL_DEFINE5(preadv, unsigned long, fd, const struct iovec __user *, vec,
+                unsigned long, vlen, u32, pos_high, u32, pos_low)
+{
+        loff_t pos = ((loff_t)pos_high << 32) | pos_low;
+        struct file *file;
+        ssize_t ret = -EBADF;
+        int fput_needed;
+
+        if (pos < 0)
+                return -EINVAL;
+
+        file = fget_light(fd, &fput_needed);
+        if (file) {
+                ret = -ESPIPE;
+                if (file->f_mode & FMODE_PREAD)
+                        ret = vfs_readv(file, vec, vlen, &pos);
+                fput_light(file, fput_needed);
+        }
+
+        if (ret > 0)
+                add_rchar(current, ret);
+        inc_syscr(current);
+        return ret;
+}
+
+SYSCALL_DEFINE5(pwritev, unsigned long, fd, const struct iovec __user *, vec,
+                unsigned long, vlen, u32, pos_high, u32, pos_low)
+{
+        loff_t pos = ((loff_t)pos_high << 32) | pos_low;
+        struct file *file;
+        ssize_t ret = -EBADF;
+        int fput_needed;
+
+        if (pos < 0)
+                return -EINVAL;
+
+        file = fget_light(fd, &fput_needed);
+        if (file) {
+                ret = -ESPIPE;
+                if (file->f_mode & FMODE_PWRITE)
+                        ret = vfs_writev(file, vec, vlen, &pos);
+                fput_light(file, fput_needed);
+        }
+
+        if (ret > 0)
+                add_wchar(current, ret);
+        inc_syscw(current);
+        return ret;
+}
+
 static ssize_t do_sendfile(int out_fd, int in_fd, loff_t *ppos,
                            size_t count, loff_t max)
 {
diff --git a/include/linux/compat.h b/include/linux/compat.h
index b880864672de..9723edd6455c 100644
--- a/include/linux/compat.h
+++ b/include/linux/compat.h
@@ -191,6 +191,12 @@ asmlinkage ssize_t compat_sys_readv(unsigned long fd,
                 const struct compat_iovec __user *vec, unsigned long vlen);
 asmlinkage ssize_t compat_sys_writev(unsigned long fd,
                 const struct compat_iovec __user *vec, unsigned long vlen);
+asmlinkage ssize_t compat_sys_preadv(unsigned long fd,
+                const struct compat_iovec __user *vec,
+                unsigned long vlen, u32 pos_high, u32 pos_low);
+asmlinkage ssize_t compat_sys_pwritev(unsigned long fd,
+                const struct compat_iovec __user *vec,
+                unsigned long vlen, u32 pos_high, u32 pos_low);
 
 int compat_do_execve(char * filename, compat_uptr_t __user *argv,
                 compat_uptr_t __user *envp, struct pt_regs * regs);
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index f9f900cfd066..b299a82a05e7 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -461,6 +461,10 @@ asmlinkage long sys_pread64(unsigned int fd, char __user *buf,
                             size_t count, loff_t pos);
 asmlinkage long sys_pwrite64(unsigned int fd, const char __user *buf,
                              size_t count, loff_t pos);
+asmlinkage long sys_preadv(unsigned long fd, const struct iovec __user *vec,
+                           unsigned long vlen, u32 pos_high, u32 pos_low);
+asmlinkage long sys_pwritev(unsigned long fd, const struct iovec __user *vec,
+                            unsigned long vlen, u32 pos_high, u32 pos_low);
 asmlinkage long sys_getcwd(char __user *buf, unsigned long size);
 asmlinkage long sys_mkdir(const char __user *pathname, int mode);
 asmlinkage long sys_chdir(const char __user *filename);