[RFC/PATCH] Add preadv and pwritev system calls.

[RFC/PATCH] Add preadv and pwritev system calls.

[Gerd Hoffmann]

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  Hi,

The attached 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.

Comments?  Reviews?  Suggestions?  Flames?

cheers,
  Gerd


[-- Attachment #2: preadv.diff --]
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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..8655487 100644
--- a/fs/compat.c
+++ b/fs/compat.c
@@ -1214,6 +1214,55 @@ 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;
+
+	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:
+	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;
+
+	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:
+	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)
 {

Re: [RFC/PATCH] Add preadv and pwritev system calls.

[Christoph Hellwig]

On Fri, Dec 12, 2008 at 12:13:43AM +0100, Gerd Hoffmann wrote:
>   Hi,
> 
> The attached 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.
> 
> Comments?  Reviews?  Suggestions?  Flames?

Looks good, but you should Cc linux-arch so that arch maintainers get
a heads up to wire up the syscalls.

> +	if (ret > 0)
> +		add_rchar(current, ret);
> +	inc_syscr(current);
> +	return ret;

Could it be that these are missing for the compat case both for the existing
readv/writev and your new syscalls?

Re: [RFC/PATCH] Add preadv and pwritev system calls.

[Gerd Hoffmann]

Christoph Hellwig wrote:
> 
> Looks good, but you should Cc linux-arch so that arch maintainers get
> a heads up to wire up the syscalls.

Will do for the next version.

>> +	if (ret > 0)
>> +		add_rchar(current, ret);
>> +	inc_syscr(current);
>> +	return ret;
> 
> Could it be that these are missing for the compat case both for the existing
> readv/writev and your new syscalls?

Yep, seems so, I can't spot them anywhere in compat.c.
I'll sort that too.

thanks,
  Gerd