preadv/pwritev: Add preadv and pwritev system calls.

f3554f4b · Gerd Hoffmann <[email protected]> · 2009-04-02 16:59:23 -07:00

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 <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Al Viro <[email protected]>
Cc: <[email protected]>
Cc: <[email protected]>
Cc: Ralf Baechle <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Commit: f3554f4bc69803ac2baaf7cf2aa4339e1f4b693e
Parents: 6949a631

Changes

8 files changed · +106 −0

File	Status	Add	Del	Content
arch/x86/ia32/ia32entry.S	modified	+2	−0	View file
arch/x86/include/asm/unistd_32.h	modified	+2	−0	View file
arch/x86/include/asm/unistd_64.h	modified	+4	−0	View file
arch/x86/kernel/syscall_table_32.S	modified	+2	−0	View file
fs/compat.c	modified	+36	−0	View file
fs/read_write.c	modified	+50	−0	View file
include/linux/compat.h	modified	+6	−0	View file
include/linux/syscalls.h	modified	+4	−0	View file

arch/x86/ia32/ia32entry.S

View file

diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S
index db0c803..a505202 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:

arch/x86/include/asm/unistd_32.h

View file

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__
 

arch/x86/include/asm/unistd_64.h

View file

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

arch/x86/kernel/syscall_table_32.S

View file

diff --git a/arch/x86/kernel/syscall_table_32.S b/arch/x86/kernel/syscall_table_32.S
index 3bdb648..ff5c873 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

fs/compat.c

View file

diff --git a/fs/compat.c b/fs/compat.c
index e04b466..7c16151 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)

fs/read_write.c

View file

diff --git a/fs/read_write.c b/fs/read_write.c
index 400fe81..6d5d8ff 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)
 {

include/linux/compat.h

View file

diff --git a/include/linux/compat.h b/include/linux/compat.h
index b880864..9723edd 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);

include/linux/syscalls.h

View file

diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index f9f900c..b299a82 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);