[PATCH v2] Add preadv and pwritev system calls.

Gerd Hoffmann
2008-12-12T14:01:39Z

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 patch sports the actual system call implementation and the windup in
the x86 system call tables. Other archs are TBD.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
---
arch/x86/ia32/ia32entry.S | 2 +
arch/x86/include/asm/unistd_32.h | 2 +
arch/x86/include/asm/unistd_64.h | 4 ++
arch/x86/kernel/syscall_table_32.S | 2 +
fs/compat.c | 61 ++++++++++++++++++++++++++++++++++++
fs/read_write.c | 48 ++++++++++++++++++++++++++++
6 files changed, 119 insertions(+), 0 deletions(-)

diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S
index 256b00b..9a8501b 100644
--- a/arch/x86/ia32/ia32entry.S
+++ b/arch/x86/ia32/ia32entry.S
@@ -826,4 +826,6 @@ 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 f2bba78..6e72d74 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 d2e415e..f818294 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 d44395f..a1a5506 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 e5f49f5..3a25cf3 100644
--- a/fs/compat.c
+++ b/fs/compat.c
@@ -1214,6 +1214,67 @@ out:
return ret;
}

+asmlinkage ssize_t
+compat_sys_preadv(unsigned long fd, const struct compat_iovec __user *vec,
+ unsigned long vlen, loff_t pos)
+{
+ struct file *file;
+ ssize_t ret = -EBADF;
+
+ if (pos < 0)
+ return -EINVAL;
+
+ file = fget(fd);
+ if (!file)
+ return -EBADF;
+
+ if (!(file->f_mode & FMODE_READ))
+ goto out;
+
+ ret = -EINVAL;
+ if (!file->f_op || (!file->f_op->aio_read && !file->f_op->read))
+ goto out;
+
+ ret = compat_do_readv_writev(READ, file, vec, vlen, &pos);
+
+out:
+ if (ret > 0)
+ add_rchar(current, ret);
+ inc_syscr(current);
+ fput(file);
+ return ret;
+}
+
+asmlinkage ssize_t
+compat_sys_pwritev(unsigned long fd, const struct compat_iovec __user *vec,
+ unsigned long vlen, loff_t pos)
+{
+ struct file *file;
+ ssize_t ret = -EBADF;
+
+ if (pos < 0)
+ return -EINVAL;
+
+ file = fget(fd);
+ if (!file)
+ return -EBADF;
+ if (!(file->f_mode & FMODE_WRITE))
+ goto out;
+
+ ret = -EINVAL;
+ if (!file->f_op || (!file->f_op->aio_write && !file->f_op->write))
+ goto out;
+
+ ret = compat_do_readv_writev(WRITE, file, vec, vlen, &pos);
+
+out:
+ if (ret > 0)
+ add_wchar(current, ret);
+ inc_syscw(current);
+ 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 969a6d9..89f273d 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -701,6 +701,54 @@ sys_writev(unsigned long fd, const struct iovec __user *vec, unsigned long vlen)
return ret;
}

+asmlinkage ssize_t sys_preadv(unsigned long fd, const struct iovec __user *vec,
+ unsigned long vlen, loff_t pos)
+{
+ 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;
+}
+
+asmlinkage ssize_t sys_pwritev(unsigned long fd, const struct iovec __user *vec,
+ unsigned long vlen, loff_t pos)
+{
+ 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)
{
--
1.5.6.5