[PATCH 2/6] vfs: vfs: Define new syscalls preadv2,pwritev2

[PATCH 2/6] vfs: vfs: Define new syscalls preadv2,pwritev2

[Christoph Hellwig]

From: Milosz Tanski <milosz@adfin.com>

New syscalls that take an flag argument.   No flags are added yet in this
patch.

Signed-off-by: Milosz Tanski <milosz@adfin.com>
[hch: rebased on top of my kiocb changes]
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Stephen Bates <stephen.bates@pmcs.com>
Tested-by: Stephen Bates <stephen.bates@pmcs.com>
Acked-by: Jeff Moyer <jmoyer@redhat.com>
---
 fs/read_write.c          | 161 ++++++++++++++++++++++++++++++++++++-----------
 include/linux/compat.h   |   6 ++
 include/linux/syscalls.h |   6 ++
 3 files changed, 138 insertions(+), 35 deletions(-)

diff --git a/fs/read_write.c b/fs/read_write.c
index 3b7577d..799d25f 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -896,15 +896,15 @@ ssize_t vfs_writev(struct file *file, const struct iovec __user *vec,
 
 EXPORT_SYMBOL(vfs_writev);
 
-SYSCALL_DEFINE3(readv, unsigned long, fd, const struct iovec __user *, vec,
-		unsigned long, vlen)
+static ssize_t do_readv(unsigned long fd, const struct iovec __user *vec,
+			unsigned long vlen, int flags)
 {
 	struct fd f = fdget_pos(fd);
 	ssize_t ret = -EBADF;
 
 	if (f.file) {
 		loff_t pos = file_pos_read(f.file);
-		ret = vfs_readv(f.file, vec, vlen, &pos, 0);
+		ret = vfs_readv(f.file, vec, vlen, &pos, flags);
 		if (ret >= 0)
 			file_pos_write(f.file, pos);
 		fdput_pos(f);
@@ -916,15 +916,15 @@ SYSCALL_DEFINE3(readv, unsigned long, fd, const struct iovec __user *, vec,
 	return ret;
 }
 
-SYSCALL_DEFINE3(writev, unsigned long, fd, const struct iovec __user *, vec,
-		unsigned long, vlen)
+static ssize_t do_writev(unsigned long fd, const struct iovec __user *vec,
+			 unsigned long vlen, int flags)
 {
 	struct fd f = fdget_pos(fd);
 	ssize_t ret = -EBADF;
 
 	if (f.file) {
 		loff_t pos = file_pos_read(f.file);
-		ret = vfs_writev(f.file, vec, vlen, &pos, 0);
+		ret = vfs_writev(f.file, vec, vlen, &pos, flags);
 		if (ret >= 0)
 			file_pos_write(f.file, pos);
 		fdput_pos(f);
@@ -942,10 +942,9 @@ static inline loff_t pos_from_hilo(unsigned long high, unsigned long low)
 	return (((loff_t)high << HALF_LONG_BITS) << HALF_LONG_BITS) | low;
 }
 
-SYSCALL_DEFINE5(preadv, unsigned long, fd, const struct iovec __user *, vec,
-		unsigned long, vlen, unsigned long, pos_l, unsigned long, pos_h)
+static ssize_t do_preadv(unsigned long fd, const struct iovec __user *vec,
+			 unsigned long vlen, loff_t pos, int flags)
 {
-	loff_t pos = pos_from_hilo(pos_h, pos_l);
 	struct fd f;
 	ssize_t ret = -EBADF;
 
@@ -956,7 +955,7 @@ SYSCALL_DEFINE5(preadv, unsigned long, fd, const struct iovec __user *, vec,
 	if (f.file) {
 		ret = -ESPIPE;
 		if (f.file->f_mode & FMODE_PREAD)
-			ret = vfs_readv(f.file, vec, vlen, &pos, 0);
+			ret = vfs_readv(f.file, vec, vlen, &pos, flags);
 		fdput(f);
 	}
 
@@ -966,10 +965,9 @@ SYSCALL_DEFINE5(preadv, unsigned long, fd, const struct iovec __user *, vec,
 	return ret;
 }
 
-SYSCALL_DEFINE5(pwritev, unsigned long, fd, const struct iovec __user *, vec,
-		unsigned long, vlen, unsigned long, pos_l, unsigned long, pos_h)
+static ssize_t do_pwritev(unsigned long fd, const struct iovec __user *vec,
+			  unsigned long vlen, loff_t pos, int flags)
 {
-	loff_t pos = pos_from_hilo(pos_h, pos_l);
 	struct fd f;
 	ssize_t ret = -EBADF;
 
@@ -980,7 +978,7 @@ SYSCALL_DEFINE5(pwritev, unsigned long, fd, const struct iovec __user *, vec,
 	if (f.file) {
 		ret = -ESPIPE;
 		if (f.file->f_mode & FMODE_PWRITE)
-			ret = vfs_writev(f.file, vec, vlen, &pos, 0);
+			ret = vfs_writev(f.file, vec, vlen, &pos, flags);
 		fdput(f);
 	}
 
@@ -990,6 +988,58 @@ SYSCALL_DEFINE5(pwritev, unsigned long, fd, const struct iovec __user *, vec,
 	return ret;
 }
 
+SYSCALL_DEFINE3(readv, unsigned long, fd, const struct iovec __user *, vec,
+		unsigned long, vlen)
+{
+	return do_readv(fd, vec, vlen, 0);
+}
+
+SYSCALL_DEFINE3(writev, unsigned long, fd, const struct iovec __user *, vec,
+		unsigned long, vlen)
+{
+	return do_writev(fd, vec, vlen, 0);
+}
+
+SYSCALL_DEFINE5(preadv, unsigned long, fd, const struct iovec __user *, vec,
+		unsigned long, vlen, unsigned long, pos_l, unsigned long, pos_h)
+{
+	loff_t pos = pos_from_hilo(pos_h, pos_l);
+
+	return do_preadv(fd, vec, vlen, pos, 0);
+}
+
+SYSCALL_DEFINE6(preadv2, unsigned long, fd, const struct iovec __user *, vec,
+		unsigned long, vlen, unsigned long, pos_l, unsigned long, pos_h,
+		int, flags)
+{
+	loff_t pos = pos_from_hilo(pos_h, pos_l);
+
+	if (pos == -1)
+		return do_readv(fd, vec, vlen, flags);
+
+	return do_preadv(fd, vec, vlen, pos, flags);
+}
+
+SYSCALL_DEFINE5(pwritev, unsigned long, fd, const struct iovec __user *, vec,
+		unsigned long, vlen, unsigned long, pos_l, unsigned long, pos_h)
+{
+	loff_t pos = pos_from_hilo(pos_h, pos_l);
+
+	return do_pwritev(fd, vec, vlen, pos, 0);
+}
+
+SYSCALL_DEFINE6(pwritev2, unsigned long, fd, const struct iovec __user *, vec,
+		unsigned long, vlen, unsigned long, pos_l, unsigned long, pos_h,
+		int, flags)
+{
+	loff_t pos = pos_from_hilo(pos_h, pos_l);
+
+	if (pos == -1)
+		return do_writev(fd, vec, vlen, flags);
+
+	return do_pwritev(fd, vec, vlen, pos, flags);
+}
+
 #ifdef CONFIG_COMPAT
 
 static ssize_t compat_do_readv_writev(int type, struct file *file,
@@ -1047,7 +1097,7 @@ out:
 
 static size_t compat_readv(struct file *file,
 			   const struct compat_iovec __user *vec,
-			   unsigned long vlen, loff_t *pos)
+			   unsigned long vlen, loff_t *pos, int flags)
 {
 	ssize_t ret = -EBADF;
 
@@ -1058,7 +1108,7 @@ static size_t compat_readv(struct file *file,
 	if (!(file->f_mode & FMODE_CAN_READ))
 		goto out;
 
-	ret = compat_do_readv_writev(READ, file, vec, vlen, pos, 0);
+	ret = compat_do_readv_writev(READ, file, vec, vlen, pos, flags);
 
 out:
 	if (ret > 0)
@@ -1067,9 +1117,9 @@ out:
 	return ret;
 }
 
-COMPAT_SYSCALL_DEFINE3(readv, compat_ulong_t, fd,
-		const struct compat_iovec __user *,vec,
-		compat_ulong_t, vlen)
+static size_t do_compat_readv(compat_ulong_t fd,
+				 const struct compat_iovec __user *vec,
+				 compat_ulong_t vlen, int flags)
 {
 	struct fd f = fdget_pos(fd);
 	ssize_t ret;
@@ -1078,16 +1128,24 @@ COMPAT_SYSCALL_DEFINE3(readv, compat_ulong_t, fd,
 	if (!f.file)
 		return -EBADF;
 	pos = f.file->f_pos;
-	ret = compat_readv(f.file, vec, vlen, &pos);
+	ret = compat_readv(f.file, vec, vlen, &pos, flags);
 	if (ret >= 0)
 		f.file->f_pos = pos;
 	fdput_pos(f);
 	return ret;
+
 }
 
-static long __compat_sys_preadv64(unsigned long fd,
+COMPAT_SYSCALL_DEFINE3(readv, compat_ulong_t, fd,
+		const struct compat_iovec __user *,vec,
+		compat_ulong_t, vlen)
+{
+	return do_compat_readv(fd, vec, vlen, 0);
+}
+
+static long do_compat_preadv64(unsigned long fd,
 				  const struct compat_iovec __user *vec,
-				  unsigned long vlen, loff_t pos)
+				  unsigned long vlen, loff_t pos, int flags)
 {
 	struct fd f;
 	ssize_t ret;
@@ -1099,7 +1157,7 @@ static long __compat_sys_preadv64(unsigned long fd,
 		return -EBADF;
 	ret = -ESPIPE;
 	if (f.file->f_mode & FMODE_PREAD)
-		ret = compat_readv(f.file, vec, vlen, &pos);
+		ret = compat_readv(f.file, vec, vlen, &pos, flags);
 	fdput(f);
 	return ret;
 }
@@ -1109,7 +1167,7 @@ COMPAT_SYSCALL_DEFINE4(preadv64, unsigned long, fd,
 		const struct compat_iovec __user *,vec,
 		unsigned long, vlen, loff_t, pos)
 {
-	return __compat_sys_preadv64(fd, vec, vlen, pos);
+	return do_compat_preadv64(fd, vec, vlen, pos, 0);
 }
 #endif
 
@@ -1119,12 +1177,25 @@ COMPAT_SYSCALL_DEFINE5(preadv, compat_ulong_t, fd,
 {
 	loff_t pos = ((loff_t)pos_high << 32) | pos_low;
 
-	return __compat_sys_preadv64(fd, vec, vlen, pos);
+	return do_compat_preadv64(fd, vec, vlen, pos, 0);
+}
+
+COMPAT_SYSCALL_DEFINE6(preadv2, compat_ulong_t, fd,
+		const struct compat_iovec __user *,vec,
+		compat_ulong_t, vlen, u32, pos_low, u32, pos_high,
+		int, flags)
+{
+	loff_t pos = ((loff_t)pos_high << 32) | pos_low;
+
+	if (pos == -1)
+		return do_compat_readv(fd, vec, vlen, flags);
+
+	return do_compat_preadv64(fd, vec, vlen, pos, flags);
 }
 
 static size_t compat_writev(struct file *file,
 			    const struct compat_iovec __user *vec,
-			    unsigned long vlen, loff_t *pos)
+			    unsigned long vlen, loff_t *pos, int flags)
 {
 	ssize_t ret = -EBADF;
 
@@ -1144,9 +1215,9 @@ out:
 	return ret;
 }
 
-COMPAT_SYSCALL_DEFINE3(writev, compat_ulong_t, fd,
-		const struct compat_iovec __user *, vec,
-		compat_ulong_t, vlen)
+static size_t do_compat_writev(compat_ulong_t fd,
+				  const struct compat_iovec __user* vec,
+				  compat_ulong_t vlen, int flags)
 {
 	struct fd f = fdget_pos(fd);
 	ssize_t ret;
@@ -1155,16 +1226,23 @@ COMPAT_SYSCALL_DEFINE3(writev, compat_ulong_t, fd,
 	if (!f.file)
 		return -EBADF;
 	pos = f.file->f_pos;
-	ret = compat_writev(f.file, vec, vlen, &pos);
+	ret = compat_writev(f.file, vec, vlen, &pos, flags);
 	if (ret >= 0)
 		f.file->f_pos = pos;
 	fdput_pos(f);
 	return ret;
 }
 
-static long __compat_sys_pwritev64(unsigned long fd,
+COMPAT_SYSCALL_DEFINE3(writev, compat_ulong_t, fd,
+		const struct compat_iovec __user *, vec,
+		compat_ulong_t, vlen)
+{
+	return do_compat_writev(fd, vec, vlen, 0);
+}
+
+static long do_compat_pwritev64(unsigned long fd,
 				   const struct compat_iovec __user *vec,
-				   unsigned long vlen, loff_t pos)
+				   unsigned long vlen, loff_t pos, int flags)
 {
 	struct fd f;
 	ssize_t ret;
@@ -1176,7 +1254,7 @@ static long __compat_sys_pwritev64(unsigned long fd,
 		return -EBADF;
 	ret = -ESPIPE;
 	if (f.file->f_mode & FMODE_PWRITE)
-		ret = compat_writev(f.file, vec, vlen, &pos);
+		ret = compat_writev(f.file, vec, vlen, &pos, flags);
 	fdput(f);
 	return ret;
 }
@@ -1186,7 +1264,7 @@ COMPAT_SYSCALL_DEFINE4(pwritev64, unsigned long, fd,
 		const struct compat_iovec __user *,vec,
 		unsigned long, vlen, loff_t, pos)
 {
-	return __compat_sys_pwritev64(fd, vec, vlen, pos);
+	return do_compat_pwritev64(fd, vec, vlen, pos, 0);
 }
 #endif
 
@@ -1196,8 +1274,21 @@ COMPAT_SYSCALL_DEFINE5(pwritev, compat_ulong_t, fd,
 {
 	loff_t pos = ((loff_t)pos_high << 32) | pos_low;
 
-	return __compat_sys_pwritev64(fd, vec, vlen, pos);
+	return do_compat_pwritev64(fd, vec, vlen, pos, 0);
+}
+
+COMPAT_SYSCALL_DEFINE6(pwritev2, compat_ulong_t, fd,
+		const struct compat_iovec __user *,vec,
+		compat_ulong_t, vlen, u32, pos_low, u32, pos_high, int, flags)
+{
+	loff_t pos = ((loff_t)pos_high << 32) | pos_low;
+
+	if (pos == -1)
+		return do_compat_writev(fd, vec, vlen, flags);
+
+	return do_compat_pwritev64(fd, vec, vlen, pos, flags);
 }
+
 #endif
 
 static ssize_t do_sendfile(int out_fd, int in_fd, loff_t *ppos,
diff --git a/include/linux/compat.h b/include/linux/compat.h
index a76c917..fe4ccd0 100644
--- a/include/linux/compat.h
+++ b/include/linux/compat.h
@@ -340,6 +340,12 @@ asmlinkage ssize_t compat_sys_preadv(compat_ulong_t fd,
 asmlinkage ssize_t compat_sys_pwritev(compat_ulong_t fd,
 		const struct compat_iovec __user *vec,
 		compat_ulong_t vlen, u32 pos_low, u32 pos_high);
+asmlinkage ssize_t compat_sys_preadv2(compat_ulong_t fd,
+		const struct compat_iovec __user *vec,
+		compat_ulong_t vlen, u32 pos_low, u32 pos_high, int flags);
+asmlinkage ssize_t compat_sys_pwritev2(compat_ulong_t fd,
+		const struct compat_iovec __user *vec,
+		compat_ulong_t vlen, u32 pos_low, u32 pos_high, int flags);
 
 #ifdef __ARCH_WANT_COMPAT_SYS_PREADV64
 asmlinkage long compat_sys_preadv64(unsigned long fd,
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 185815c..d795472 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -575,8 +575,14 @@ 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, unsigned long pos_l, unsigned long pos_h);
+asmlinkage long sys_preadv2(unsigned long fd, const struct iovec __user *vec,
+			    unsigned long vlen, unsigned long pos_l, unsigned long pos_h,
+			    int flags);
 asmlinkage long sys_pwritev(unsigned long fd, const struct iovec __user *vec,
 			    unsigned long vlen, unsigned long pos_l, unsigned long pos_h);
+asmlinkage long sys_pwritev2(unsigned long fd, const struct iovec __user *vec,
+			    unsigned long vlen, unsigned long pos_l, unsigned long pos_h,
+			    int flags);
 asmlinkage long sys_getcwd(char __user *buf, unsigned long size);
 asmlinkage long sys_mkdir(const char __user *pathname, umode_t mode);
 asmlinkage long sys_chdir(const char __user *filename);
-- 
2.1.4

Re: [PATCH 2/6] vfs: vfs: Define new syscalls preadv2,pwritev2

[Michael Kerrisk (man-pages)]

Hi Christoph,

On 03/03/2016 04:03 PM, Christoph Hellwig wrote:
> From: Milosz Tanski <milosz@adfin.com>
> 
> New syscalls that take an flag argument.   No flags are added yet in this
> patch.

Are there some man pages patches for these proposed system calls?

Thanks,

Michael


> Signed-off-by: Milosz Tanski <milosz@adfin.com>
> [hch: rebased on top of my kiocb changes]
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> Reviewed-by: Stephen Bates <stephen.bates@pmcs.com>
> Tested-by: Stephen Bates <stephen.bates@pmcs.com>
> Acked-by: Jeff Moyer <jmoyer@redhat.com>
> ---
>  fs/read_write.c          | 161 ++++++++++++++++++++++++++++++++++++-----------
>  include/linux/compat.h   |   6 ++
>  include/linux/syscalls.h |   6 ++
>  3 files changed, 138 insertions(+), 35 deletions(-)
> 
> diff --git a/fs/read_write.c b/fs/read_write.c
> index 3b7577d..799d25f 100644
> --- a/fs/read_write.c
> +++ b/fs/read_write.c
> @@ -896,15 +896,15 @@ ssize_t vfs_writev(struct file *file, const struct iovec __user *vec,
>  
>  EXPORT_SYMBOL(vfs_writev);
>  
> -SYSCALL_DEFINE3(readv, unsigned long, fd, const struct iovec __user *, vec,
> -		unsigned long, vlen)
> +static ssize_t do_readv(unsigned long fd, const struct iovec __user *vec,
> +			unsigned long vlen, int flags)
>  {
>  	struct fd f = fdget_pos(fd);
>  	ssize_t ret = -EBADF;
>  
>  	if (f.file) {
>  		loff_t pos = file_pos_read(f.file);
> -		ret = vfs_readv(f.file, vec, vlen, &pos, 0);
> +		ret = vfs_readv(f.file, vec, vlen, &pos, flags);
>  		if (ret >= 0)
>  			file_pos_write(f.file, pos);
>  		fdput_pos(f);
> @@ -916,15 +916,15 @@ SYSCALL_DEFINE3(readv, unsigned long, fd, const struct iovec __user *, vec,
>  	return ret;
>  }
>  
> -SYSCALL_DEFINE3(writev, unsigned long, fd, const struct iovec __user *, vec,
> -		unsigned long, vlen)
> +static ssize_t do_writev(unsigned long fd, const struct iovec __user *vec,
> +			 unsigned long vlen, int flags)
>  {
>  	struct fd f = fdget_pos(fd);
>  	ssize_t ret = -EBADF;
>  
>  	if (f.file) {
>  		loff_t pos = file_pos_read(f.file);
> -		ret = vfs_writev(f.file, vec, vlen, &pos, 0);
> +		ret = vfs_writev(f.file, vec, vlen, &pos, flags);
>  		if (ret >= 0)
>  			file_pos_write(f.file, pos);
>  		fdput_pos(f);
> @@ -942,10 +942,9 @@ static inline loff_t pos_from_hilo(unsigned long high, unsigned long low)
>  	return (((loff_t)high << HALF_LONG_BITS) << HALF_LONG_BITS) | low;
>  }
>  
> -SYSCALL_DEFINE5(preadv, unsigned long, fd, const struct iovec __user *, vec,
> -		unsigned long, vlen, unsigned long, pos_l, unsigned long, pos_h)
> +static ssize_t do_preadv(unsigned long fd, const struct iovec __user *vec,
> +			 unsigned long vlen, loff_t pos, int flags)
>  {
> -	loff_t pos = pos_from_hilo(pos_h, pos_l);
>  	struct fd f;
>  	ssize_t ret = -EBADF;
>  
> @@ -956,7 +955,7 @@ SYSCALL_DEFINE5(preadv, unsigned long, fd, const struct iovec __user *, vec,
>  	if (f.file) {
>  		ret = -ESPIPE;
>  		if (f.file->f_mode & FMODE_PREAD)
> -			ret = vfs_readv(f.file, vec, vlen, &pos, 0);
> +			ret = vfs_readv(f.file, vec, vlen, &pos, flags);
>  		fdput(f);
>  	}
>  
> @@ -966,10 +965,9 @@ SYSCALL_DEFINE5(preadv, unsigned long, fd, const struct iovec __user *, vec,
>  	return ret;
>  }
>  
> -SYSCALL_DEFINE5(pwritev, unsigned long, fd, const struct iovec __user *, vec,
> -		unsigned long, vlen, unsigned long, pos_l, unsigned long, pos_h)
> +static ssize_t do_pwritev(unsigned long fd, const struct iovec __user *vec,
> +			  unsigned long vlen, loff_t pos, int flags)
>  {
> -	loff_t pos = pos_from_hilo(pos_h, pos_l);
>  	struct fd f;
>  	ssize_t ret = -EBADF;
>  
> @@ -980,7 +978,7 @@ SYSCALL_DEFINE5(pwritev, unsigned long, fd, const struct iovec __user *, vec,
>  	if (f.file) {
>  		ret = -ESPIPE;
>  		if (f.file->f_mode & FMODE_PWRITE)
> -			ret = vfs_writev(f.file, vec, vlen, &pos, 0);
> +			ret = vfs_writev(f.file, vec, vlen, &pos, flags);
>  		fdput(f);
>  	}
>  
> @@ -990,6 +988,58 @@ SYSCALL_DEFINE5(pwritev, unsigned long, fd, const struct iovec __user *, vec,
>  	return ret;
>  }
>  
> +SYSCALL_DEFINE3(readv, unsigned long, fd, const struct iovec __user *, vec,
> +		unsigned long, vlen)
> +{
> +	return do_readv(fd, vec, vlen, 0);
> +}
> +
> +SYSCALL_DEFINE3(writev, unsigned long, fd, const struct iovec __user *, vec,
> +		unsigned long, vlen)
> +{
> +	return do_writev(fd, vec, vlen, 0);
> +}
> +
> +SYSCALL_DEFINE5(preadv, unsigned long, fd, const struct iovec __user *, vec,
> +		unsigned long, vlen, unsigned long, pos_l, unsigned long, pos_h)
> +{
> +	loff_t pos = pos_from_hilo(pos_h, pos_l);
> +
> +	return do_preadv(fd, vec, vlen, pos, 0);
> +}
> +
> +SYSCALL_DEFINE6(preadv2, unsigned long, fd, const struct iovec __user *, vec,
> +		unsigned long, vlen, unsigned long, pos_l, unsigned long, pos_h,
> +		int, flags)
> +{
> +	loff_t pos = pos_from_hilo(pos_h, pos_l);
> +
> +	if (pos == -1)
> +		return do_readv(fd, vec, vlen, flags);
> +
> +	return do_preadv(fd, vec, vlen, pos, flags);
> +}
> +
> +SYSCALL_DEFINE5(pwritev, unsigned long, fd, const struct iovec __user *, vec,
> +		unsigned long, vlen, unsigned long, pos_l, unsigned long, pos_h)
> +{
> +	loff_t pos = pos_from_hilo(pos_h, pos_l);
> +
> +	return do_pwritev(fd, vec, vlen, pos, 0);
> +}
> +
> +SYSCALL_DEFINE6(pwritev2, unsigned long, fd, const struct iovec __user *, vec,
> +		unsigned long, vlen, unsigned long, pos_l, unsigned long, pos_h,
> +		int, flags)
> +{
> +	loff_t pos = pos_from_hilo(pos_h, pos_l);
> +
> +	if (pos == -1)
> +		return do_writev(fd, vec, vlen, flags);
> +
> +	return do_pwritev(fd, vec, vlen, pos, flags);
> +}
> +
>  #ifdef CONFIG_COMPAT
>  
>  static ssize_t compat_do_readv_writev(int type, struct file *file,
> @@ -1047,7 +1097,7 @@ out:
>  
>  static size_t compat_readv(struct file *file,
>  			   const struct compat_iovec __user *vec,
> -			   unsigned long vlen, loff_t *pos)
> +			   unsigned long vlen, loff_t *pos, int flags)
>  {
>  	ssize_t ret = -EBADF;
>  
> @@ -1058,7 +1108,7 @@ static size_t compat_readv(struct file *file,
>  	if (!(file->f_mode & FMODE_CAN_READ))
>  		goto out;
>  
> -	ret = compat_do_readv_writev(READ, file, vec, vlen, pos, 0);
> +	ret = compat_do_readv_writev(READ, file, vec, vlen, pos, flags);
>  
>  out:
>  	if (ret > 0)
> @@ -1067,9 +1117,9 @@ out:
>  	return ret;
>  }
>  
> -COMPAT_SYSCALL_DEFINE3(readv, compat_ulong_t, fd,
> -		const struct compat_iovec __user *,vec,
> -		compat_ulong_t, vlen)
> +static size_t do_compat_readv(compat_ulong_t fd,
> +				 const struct compat_iovec __user *vec,
> +				 compat_ulong_t vlen, int flags)
>  {
>  	struct fd f = fdget_pos(fd);
>  	ssize_t ret;
> @@ -1078,16 +1128,24 @@ COMPAT_SYSCALL_DEFINE3(readv, compat_ulong_t, fd,
>  	if (!f.file)
>  		return -EBADF;
>  	pos = f.file->f_pos;
> -	ret = compat_readv(f.file, vec, vlen, &pos);
> +	ret = compat_readv(f.file, vec, vlen, &pos, flags);
>  	if (ret >= 0)
>  		f.file->f_pos = pos;
>  	fdput_pos(f);
>  	return ret;
> +
>  }
>  
> -static long __compat_sys_preadv64(unsigned long fd,
> +COMPAT_SYSCALL_DEFINE3(readv, compat_ulong_t, fd,
> +		const struct compat_iovec __user *,vec,
> +		compat_ulong_t, vlen)
> +{
> +	return do_compat_readv(fd, vec, vlen, 0);
> +}
> +
> +static long do_compat_preadv64(unsigned long fd,
>  				  const struct compat_iovec __user *vec,
> -				  unsigned long vlen, loff_t pos)
> +				  unsigned long vlen, loff_t pos, int flags)
>  {
>  	struct fd f;
>  	ssize_t ret;
> @@ -1099,7 +1157,7 @@ static long __compat_sys_preadv64(unsigned long fd,
>  		return -EBADF;
>  	ret = -ESPIPE;
>  	if (f.file->f_mode & FMODE_PREAD)
> -		ret = compat_readv(f.file, vec, vlen, &pos);
> +		ret = compat_readv(f.file, vec, vlen, &pos, flags);
>  	fdput(f);
>  	return ret;
>  }
> @@ -1109,7 +1167,7 @@ COMPAT_SYSCALL_DEFINE4(preadv64, unsigned long, fd,
>  		const struct compat_iovec __user *,vec,
>  		unsigned long, vlen, loff_t, pos)
>  {
> -	return __compat_sys_preadv64(fd, vec, vlen, pos);
> +	return do_compat_preadv64(fd, vec, vlen, pos, 0);
>  }
>  #endif
>  
> @@ -1119,12 +1177,25 @@ COMPAT_SYSCALL_DEFINE5(preadv, compat_ulong_t, fd,
>  {
>  	loff_t pos = ((loff_t)pos_high << 32) | pos_low;
>  
> -	return __compat_sys_preadv64(fd, vec, vlen, pos);
> +	return do_compat_preadv64(fd, vec, vlen, pos, 0);
> +}
> +
> +COMPAT_SYSCALL_DEFINE6(preadv2, compat_ulong_t, fd,
> +		const struct compat_iovec __user *,vec,
> +		compat_ulong_t, vlen, u32, pos_low, u32, pos_high,
> +		int, flags)
> +{
> +	loff_t pos = ((loff_t)pos_high << 32) | pos_low;
> +
> +	if (pos == -1)
> +		return do_compat_readv(fd, vec, vlen, flags);
> +
> +	return do_compat_preadv64(fd, vec, vlen, pos, flags);
>  }
>  
>  static size_t compat_writev(struct file *file,
>  			    const struct compat_iovec __user *vec,
> -			    unsigned long vlen, loff_t *pos)
> +			    unsigned long vlen, loff_t *pos, int flags)
>  {
>  	ssize_t ret = -EBADF;
>  
> @@ -1144,9 +1215,9 @@ out:
>  	return ret;
>  }
>  
> -COMPAT_SYSCALL_DEFINE3(writev, compat_ulong_t, fd,
> -		const struct compat_iovec __user *, vec,
> -		compat_ulong_t, vlen)
> +static size_t do_compat_writev(compat_ulong_t fd,
> +				  const struct compat_iovec __user* vec,
> +				  compat_ulong_t vlen, int flags)
>  {
>  	struct fd f = fdget_pos(fd);
>  	ssize_t ret;
> @@ -1155,16 +1226,23 @@ COMPAT_SYSCALL_DEFINE3(writev, compat_ulong_t, fd,
>  	if (!f.file)
>  		return -EBADF;
>  	pos = f.file->f_pos;
> -	ret = compat_writev(f.file, vec, vlen, &pos);
> +	ret = compat_writev(f.file, vec, vlen, &pos, flags);
>  	if (ret >= 0)
>  		f.file->f_pos = pos;
>  	fdput_pos(f);
>  	return ret;
>  }
>  
> -static long __compat_sys_pwritev64(unsigned long fd,
> +COMPAT_SYSCALL_DEFINE3(writev, compat_ulong_t, fd,
> +		const struct compat_iovec __user *, vec,
> +		compat_ulong_t, vlen)
> +{
> +	return do_compat_writev(fd, vec, vlen, 0);
> +}
> +
> +static long do_compat_pwritev64(unsigned long fd,
>  				   const struct compat_iovec __user *vec,
> -				   unsigned long vlen, loff_t pos)
> +				   unsigned long vlen, loff_t pos, int flags)
>  {
>  	struct fd f;
>  	ssize_t ret;
> @@ -1176,7 +1254,7 @@ static long __compat_sys_pwritev64(unsigned long fd,
>  		return -EBADF;
>  	ret = -ESPIPE;
>  	if (f.file->f_mode & FMODE_PWRITE)
> -		ret = compat_writev(f.file, vec, vlen, &pos);
> +		ret = compat_writev(f.file, vec, vlen, &pos, flags);
>  	fdput(f);
>  	return ret;
>  }
> @@ -1186,7 +1264,7 @@ COMPAT_SYSCALL_DEFINE4(pwritev64, unsigned long, fd,
>  		const struct compat_iovec __user *,vec,
>  		unsigned long, vlen, loff_t, pos)
>  {
> -	return __compat_sys_pwritev64(fd, vec, vlen, pos);
> +	return do_compat_pwritev64(fd, vec, vlen, pos, 0);
>  }
>  #endif
>  
> @@ -1196,8 +1274,21 @@ COMPAT_SYSCALL_DEFINE5(pwritev, compat_ulong_t, fd,
>  {
>  	loff_t pos = ((loff_t)pos_high << 32) | pos_low;
>  
> -	return __compat_sys_pwritev64(fd, vec, vlen, pos);
> +	return do_compat_pwritev64(fd, vec, vlen, pos, 0);
> +}
> +
> +COMPAT_SYSCALL_DEFINE6(pwritev2, compat_ulong_t, fd,
> +		const struct compat_iovec __user *,vec,
> +		compat_ulong_t, vlen, u32, pos_low, u32, pos_high, int, flags)
> +{
> +	loff_t pos = ((loff_t)pos_high << 32) | pos_low;
> +
> +	if (pos == -1)
> +		return do_compat_writev(fd, vec, vlen, flags);
> +
> +	return do_compat_pwritev64(fd, vec, vlen, pos, flags);
>  }
> +
>  #endif
>  
>  static ssize_t do_sendfile(int out_fd, int in_fd, loff_t *ppos,
> diff --git a/include/linux/compat.h b/include/linux/compat.h
> index a76c917..fe4ccd0 100644
> --- a/include/linux/compat.h
> +++ b/include/linux/compat.h
> @@ -340,6 +340,12 @@ asmlinkage ssize_t compat_sys_preadv(compat_ulong_t fd,
>  asmlinkage ssize_t compat_sys_pwritev(compat_ulong_t fd,
>  		const struct compat_iovec __user *vec,
>  		compat_ulong_t vlen, u32 pos_low, u32 pos_high);
> +asmlinkage ssize_t compat_sys_preadv2(compat_ulong_t fd,
> +		const struct compat_iovec __user *vec,
> +		compat_ulong_t vlen, u32 pos_low, u32 pos_high, int flags);
> +asmlinkage ssize_t compat_sys_pwritev2(compat_ulong_t fd,
> +		const struct compat_iovec __user *vec,
> +		compat_ulong_t vlen, u32 pos_low, u32 pos_high, int flags);
>  
>  #ifdef __ARCH_WANT_COMPAT_SYS_PREADV64
>  asmlinkage long compat_sys_preadv64(unsigned long fd,
> diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
> index 185815c..d795472 100644
> --- a/include/linux/syscalls.h
> +++ b/include/linux/syscalls.h
> @@ -575,8 +575,14 @@ 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, unsigned long pos_l, unsigned long pos_h);
> +asmlinkage long sys_preadv2(unsigned long fd, const struct iovec __user *vec,
> +			    unsigned long vlen, unsigned long pos_l, unsigned long pos_h,
> +			    int flags);
>  asmlinkage long sys_pwritev(unsigned long fd, const struct iovec __user *vec,
>  			    unsigned long vlen, unsigned long pos_l, unsigned long pos_h);
> +asmlinkage long sys_pwritev2(unsigned long fd, const struct iovec __user *vec,
> +			    unsigned long vlen, unsigned long pos_l, unsigned long pos_h,
> +			    int flags);
>  asmlinkage long sys_getcwd(char __user *buf, unsigned long size);
>  asmlinkage long sys_mkdir(const char __user *pathname, umode_t mode);
>  asmlinkage long sys_chdir(const char __user *filename);
> 


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/

Re: [PATCH 2/6] vfs: vfs: Define new syscalls preadv2,pwritev2

[Christoph Hellwig]

On Thu, Mar 10, 2016 at 07:15:04PM +0100, Michael Kerrisk (man-pages) wrote:
> Hi Christoph,
> 
> On 03/03/2016 04:03 PM, Christoph Hellwig wrote:
> > From: Milosz Tanski <milosz@adfin.com>
> > 
> > New syscalls that take an flag argument.   No flags are added yet in this
> > patch.
> 
> Are there some man pages patches for these proposed system calls?

This is what I have:

---
>From d33a02d56f447a6cb223b3964e1dd894f2921d5c Mon Sep 17 00:00:00 2001
From: Milosz Tanski <milosz@adfin.com>
Date: Fri, 11 Mar 2016 10:52:31 +0100
Subject: add preadv2/pwritev2 documentation

New syscalls that are a variation on the preadv/pwritev but support an extra
flag argument.

Signed-off-by: Milosz Tanski <milosz@adfin.com>
[hch: added RWF_HIPRI documentation]
Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 man2/readv.2 | 63 +++++++++++++++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 54 insertions(+), 9 deletions(-)

diff --git a/man2/readv.2 b/man2/readv.2
index 93f2b6f..5cba5e2 100644
--- a/man2/readv.2
+++ b/man2/readv.2
@@ -45,6 +45,12 @@ readv, writev, preadv, pwritev \- read or write data into multiple buffers
 .sp
 .BI "ssize_t pwritev(int " fd ", const struct iovec *" iov ", int " iovcnt ,
 .BI "                off_t " offset );
+.sp
+.BI "ssize_t preadv2(int " fd ", const struct iovec *" iov ", int " iovcnt ,
+.BI "                off_t " offset ", int " flags );
+.sp
+.BI "ssize_t pwritev2(int " fd ", const struct iovec *" iov ", int " iovcnt ,
+.BI "                 off_t " offset ", int " flags );
 .fi
 .sp
 .in -4n
@@ -166,9 +172,9 @@ The
 system call combines the functionality of
 .BR writev ()
 and
-.BR pwrite (2).
+.BR pwrite (2) "."
 It performs the same task as
-.BR writev (),
+.BR writev () ","
 but adds a fourth argument,
 .IR offset ,
 which specifies the file offset at which the output operation
@@ -178,15 +184,43 @@ The file offset is not changed by these system calls.
 The file referred to by
 .I fd
 must be capable of seeking.
+.SS preadv2() and pwritev2()
+
+This pair of system calls has similar functionality to the
+.BR preadv ()
+and
+.BR pwritev ()
+calls, but adds a fifth argument, \fIflags\fP, which modifies the behavior on a per call basis.
+
+Like the
+.BR preadv ()
+and
+.BR pwritev ()
+calls, they accept an \fIoffset\fP argument. Unlike those calls, if the \fIoffset\fP argument is set to -1 then the current file offset is used and updated.
+
+The \fIflags\fP arguments to
+.BR preadv2 ()
+and
+.BR pwritev2 ()
+contains a bitwise OR of one or more of the following flags:
+.TP
+.BR RWF_HIPRI " (since Linux 4.6)"
+High priority read/write.  Allows block based filesystems to use polling of the
+device, which provides lower latency, but may use additional ressources.  (Currently
+only usable on a file descriptor opened using the
+.BR O_DIRECT " flag)."
+
 .SH RETURN VALUE
 On success,
-.BR readv ()
-and
+.BR readv () ","
 .BR preadv ()
-return the number of bytes read;
-.BR writev ()
 and
+.BR preadv2 ()
+return the number of bytes read;
+.BR writev () ","
 .BR pwritev ()
+and
+.BR pwritev2 ()
 return the number of bytes written.
 
 Note that is not an error for a successful call to transfer fewer bytes
@@ -202,9 +236,11 @@ The errors are as given for
 and
 .BR write (2).
 Furthermore,
-.BR preadv ()
-and
+.BR preadv () ","
+.BR preadv2 () ","
 .BR pwritev ()
+and
+.BR pwritev2 ()
 can also fail for the same reasons as
 .BR lseek (2).
 Additionally, the following error is defined:
@@ -218,12 +254,17 @@ value.
 .TP
 .B EINVAL
 The vector count \fIiovcnt\fP is less than zero or greater than the
-permitted maximum.
+permitted maximum. Or, an unknown flag is specified in \fIflags\fP.
 .SH VERSIONS
 .BR preadv ()
 and
 .BR pwritev ()
 first appeared in Linux 2.6.30; library support was added in glibc 2.10.
+.sp
+.BR preadv2 ()
+and
+.BR pwritev2 ()
+first appeared in Linux 4.6
 .SH CONFORMING TO
 .BR readv (),
 .BR writev ():
@@ -237,6 +278,10 @@ POSIX.1-2001, POSIX.1-2008,
 .BR preadv (),
 .BR pwritev ():
 nonstandard, but present also on the modern BSDs.
+.sp
+.BR preadv2 (),
+.BR pwritev2 ():
+nonstandard, Linux extension.
 .SH NOTES
 POSIX.1 allows an implementation to place a limit on
 the number of items that can be passed in
-- 
2.1.4

Re: [PATCH 2/6] vfs: vfs: Define new syscalls preadv2,pwritev2

[Michael Kerrisk (man-pages)]

Hello Christoph,

On 03/11/2016 09:53 AM, Christoph Hellwig wrote:
> On Thu, Mar 10, 2016 at 07:15:04PM +0100, Michael Kerrisk (man-pages) wrote:
>> Hi Christoph,
>>
>> On 03/03/2016 04:03 PM, Christoph Hellwig wrote:
>>> From: Milosz Tanski <milosz@adfin.com>
>>>
>>> New syscalls that take an flag argument.   No flags are added yet in this
>>> patch.
>>
>> Are there some man pages patches for these proposed system calls?
> 
> This is what I have:

Thanks. I applied the patch, but I see one point where the doc
and code differ, and I suspect that the code needs to be fixed.
See below.

> ---
>>>From d33a02d56f447a6cb223b3964e1dd894f2921d5c Mon Sep 17 00:00:00 2001
> From: Milosz Tanski <milosz@adfin.com>
> Date: Fri, 11 Mar 2016 10:52:31 +0100
> Subject: add preadv2/pwritev2 documentation
> 
> New syscalls that are a variation on the preadv/pwritev but support an extra
> flag argument.
> 
> Signed-off-by: Milosz Tanski <milosz@adfin.com>
> [hch: added RWF_HIPRI documentation]
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  man2/readv.2 | 63 +++++++++++++++++++++++++++++++++++++++++++++++++++---------
>  1 file changed, 54 insertions(+), 9 deletions(-)
> 
> diff --git a/man2/readv.2 b/man2/readv.2
> index 93f2b6f..5cba5e2 100644
> --- a/man2/readv.2
> +++ b/man2/readv.2
> @@ -45,6 +45,12 @@ readv, writev, preadv, pwritev \- read or write data into multiple buffers
>  .sp
>  .BI "ssize_t pwritev(int " fd ", const struct iovec *" iov ", int " iovcnt ,
>  .BI "                off_t " offset );
> +.sp
> +.BI "ssize_t preadv2(int " fd ", const struct iovec *" iov ", int " iovcnt ,
> +.BI "                off_t " offset ", int " flags );
> +.sp
> +.BI "ssize_t pwritev2(int " fd ", const struct iovec *" iov ", int " iovcnt ,
> +.BI "                 off_t " offset ", int " flags );
>  .fi
>  .sp
>  .in -4n
> @@ -166,9 +172,9 @@ The
>  system call combines the functionality of
>  .BR writev ()
>  and
> -.BR pwrite (2).
> +.BR pwrite (2) "."
>  It performs the same task as
> -.BR writev (),
> +.BR writev () ","
>  but adds a fourth argument,
>  .IR offset ,
>  which specifies the file offset at which the output operation
> @@ -178,15 +184,43 @@ The file offset is not changed by these system calls.
>  The file referred to by
>  .I fd
>  must be capable of seeking.
> +.SS preadv2() and pwritev2()
> +
> +This pair of system calls has similar functionality to the
> +.BR preadv ()
> +and
> +.BR pwritev ()
> +calls, but adds a fifth argument, \fIflags\fP, which modifies the behavior on a per call basis.
> +
> +Like the
> +.BR preadv ()
> +and
> +.BR pwritev ()
> +calls, they accept an \fIoffset\fP argument. Unlike those calls, if the \fIoffset\fP argument is set to -1 then the current file offset is used and updated.
> +
> +The \fIflags\fP arguments to
> +.BR preadv2 ()
> +and
> +.BR pwritev2 ()
> +contains a bitwise OR of one or more of the following flags:
> +.TP
> +.BR RWF_HIPRI " (since Linux 4.6)"
> +High priority read/write.  Allows block based filesystems to use polling of the
> +device, which provides lower latency, but may use additional ressources.  (Currently
> +only usable on a file descriptor opened using the
> +.BR O_DIRECT " flag)."
> +
>  .SH RETURN VALUE
>  On success,
> -.BR readv ()
> -and
> +.BR readv () ","
>  .BR preadv ()
> -return the number of bytes read;
> -.BR writev ()
>  and
> +.BR preadv2 ()
> +return the number of bytes read;
> +.BR writev () ","
>  .BR pwritev ()
> +and
> +.BR pwritev2 ()
>  return the number of bytes written.
>  
>  Note that is not an error for a successful call to transfer fewer bytes
> @@ -202,9 +236,11 @@ The errors are as given for
>  and
>  .BR write (2).
>  Furthermore,
> -.BR preadv ()
> -and
> +.BR preadv () ","
> +.BR preadv2 () ","
>  .BR pwritev ()
> +and
> +.BR pwritev2 ()
>  can also fail for the same reasons as
>  .BR lseek (2).
>  Additionally, the following error is defined:
> @@ -218,12 +254,17 @@ value.
>  .TP
>  .B EINVAL
>  The vector count \fIiovcnt\fP is less than zero or greater than the
> -permitted maximum.
> +permitted maximum. Or, an unknown flag is specified in \fIflags\fP.

In the case described in the last sentence, the code currently appears
to be returning EOPNOTSUPP. EINVAL is more usual here, so I think the
code needs adjusting. Your thoughts?

Cheers,

Michael

-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/

Re: [PATCH 2/6] vfs: vfs: Define new syscalls preadv2,pwritev2

[Christoph Hellwig]

On Mon, Apr 18, 2016 at 02:51:50PM +0100, Michael Kerrisk (man-pages) wrote:
> Thanks. I applied the patch, but I see one point where the doc
> and code differ, and I suspect that the code needs to be fixed.
> See below.

> >  .TP
> >  .B EINVAL
> >  The vector count \fIiovcnt\fP is less than zero or greater than the
> > -permitted maximum.
> > +permitted maximum. Or, an unknown flag is specified in \fIflags\fP.
> 
> In the case described in the last sentence, the code currently appears
> to be returning EOPNOTSUPP. EINVAL is more usual here, so I think the
> code needs adjusting. Your thoughts?

I'd rather update the man page - EOPNOTSUPP is a much more descriptive
error code for this case.  I'll send you a patch.

Re: [PATCH 2/6] vfs: vfs: Define new syscalls preadv2,pwritev2

[Michael Kerrisk (man-pages)]

Hi Christoph,

On 25 April 2016 at 10:47, Christoph Hellwig <hch@infradead.org> wrote:
> On Mon, Apr 18, 2016 at 02:51:50PM +0100, Michael Kerrisk (man-pages) wrote:
>> Thanks. I applied the patch, but I see one point where the doc
>> and code differ, and I suspect that the code needs to be fixed.
>> See below.
>
>> >  .TP
>> >  .B EINVAL
>> >  The vector count \fIiovcnt\fP is less than zero or greater than the
>> > -permitted maximum.
>> > +permitted maximum. Or, an unknown flag is specified in \fIflags\fP.
>>
>> In the case described in the last sentence, the code currently appears
>> to be returning EOPNOTSUPP. EINVAL is more usual here, so I think the
>> code needs adjusting. Your thoughts?
>
> I'd rather update the man page - EOPNOTSUPP is a much more descriptive
> error code for this case.  I'll send you a patch.

Unless I'm misunderstanding something here, you're proposing something
very inconsistent. The standard error for unknown flag bits is EINVAL.
This is so for dozens of systems calls (check the man pages; you might
find a rare exception, but that's the point, they are exceptions). It
seems to me here that it's really the implementation that needs
fixing, not the man page!

Cheers,

Michael




-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/

Re: [PATCH 2/6] vfs: vfs: Define new syscalls preadv2,pwritev2

[Christoph Hellwig]

On Mon, Apr 25, 2016 at 07:35:36PM +0200, Michael Kerrisk (man-pages) wrote:
> > I'd rather update the man page - EOPNOTSUPP is a much more descriptive
> > error code for this case.  I'll send you a patch.
> 
> Unless I'm misunderstanding something here, you're proposing something
> very inconsistent. The standard error for unknown flag bits is EINVAL.
> This is so for dozens of systems calls (check the man pages; you might
> find a rare exception, but that's the point, they are exceptions). It
> seems to me here that it's really the implementation that needs
> fixing, not the man page!

For new filesystem calls we try to use EOPNOTSUPP as much as possible,
e.g. fallocate.

[PATCH 4/6] vfs: add the RWF_HIPRI flag for preadv2/pwritev2

[Christoph Hellwig]

This adds a flag that tells the file system that this is a high priority
request for which it's worth to poll the hardware.  The flag is purely
advisory and can be ignored if not supported.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Stephen Bates <stephen.bates@pmcs.com>
Tested-by: Stephen Bates <stephen.bates@pmcs.com>
Acked-by: Jeff Moyer <jmoyer@redhat.com>
---
 fs/read_write.c         | 6 ++++--
 include/linux/fs.h      | 1 +
 include/uapi/linux/fs.h | 3 +++
 3 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/fs/read_write.c b/fs/read_write.c
index 799d25f..cf377cf 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -698,10 +698,12 @@ static ssize_t do_iter_readv_writev(struct file *filp, struct iov_iter *iter,
 	struct kiocb kiocb;
 	ssize_t ret;
 
-	if (flags)
+	if (flags & ~RWF_HIPRI)
 		return -EOPNOTSUPP;
 
 	init_sync_kiocb(&kiocb, filp);
+	if (flags & RWF_HIPRI)
+		kiocb.ki_flags |= IOCB_HIPRI;
 	kiocb.ki_pos = *ppos;
 
 	ret = fn(&kiocb, iter);
@@ -716,7 +718,7 @@ static ssize_t do_loop_readv_writev(struct file *filp, struct iov_iter *iter,
 {
 	ssize_t ret = 0;
 
-	if (flags)
+	if (flags & ~RWF_HIPRI)
 		return -EOPNOTSUPP;
 
 	while (iov_iter_count(iter)) {
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 875277a..a1f731c 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -320,6 +320,7 @@ struct writeback_control;
 #define IOCB_EVENTFD		(1 << 0)
 #define IOCB_APPEND		(1 << 1)
 #define IOCB_DIRECT		(1 << 2)
+#define IOCB_HIPRI		(1 << 3)
 
 struct kiocb {
 	struct file		*ki_filp;
diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
index 149bec8..d246339 100644
--- a/include/uapi/linux/fs.h
+++ b/include/uapi/linux/fs.h
@@ -304,4 +304,7 @@ struct fsxattr {
 #define SYNC_FILE_RANGE_WRITE		2
 #define SYNC_FILE_RANGE_WAIT_AFTER	4
 
+/* flags for preadv2/pwritev2: */
+#define RWF_HIPRI			0x00000001 /* high priority request, poll if possible */
+
 #endif /* _UAPI_LINUX_FS_H */
-- 
2.1.4

Re: [PATCH 4/6] vfs: add the RWF_HIPRI flag for preadv2/pwritev2

[NeilBrown]

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On Fri, Mar 04 2016, Christoph Hellwig wrote:

> This adds a flag that tells the file system that this is a high priority
> request for which it's worth to poll the hardware.  The flag is purely
> advisory and can be ignored if not supported.

Here you say the flag is "advice".

>  
> +/* flags for preadv2/pwritev2: */
> +#define RWF_HIPRI			0x00000001 /* high priority request, poll if possible */

This text makes it sound like a firm "request" ("if possible").

In the man page posted separately it says:

+.BR RWF_HIPRI " (since Linux 4.6)"
+High priority read/write.  Allows block based filesystems to use polling of the
+device, which provides lower latency, but may use additional ressources.  (Currently
+only usable on a file descriptor opened using the
+.BR O_DIRECT " flag)."

So now it "allows", which is different again.

The differences may be subtle, but consistency is nice.

Also in that man page fragment:

> provides lower latency, but may use additional ressources

Is this a "latency vs throughput" trade-off, or something more subtle?
It would be nice to make the decision process as obvious as possible for
the developer considering the use of this flag.

(and s/ressources/resources/)

NeilBrown

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Re: [PATCH 4/6] vfs: add the RWF_HIPRI flag for preadv2/pwritev2

[Christoph Hellwig]

On Mon, May 09, 2016 at 07:47:04AM +1000, NeilBrown wrote:
> On Fri, Mar 04 2016, Christoph Hellwig wrote:
> 
> > This adds a flag that tells the file system that this is a high priority
> > request for which it's worth to poll the hardware.  The flag is purely
> > advisory and can be ignored if not supported.
> 
> Here you say the flag is "advice".
> 
> >  
> > +/* flags for preadv2/pwritev2: */
> > +#define RWF_HIPRI			0x00000001 /* high priority request, poll if possible */
> 
> This text makes it sound like a firm "request" ("if possible").

"request" here is in the sense of an I/O request.  Better wording
highly welcome.

> 
> > provides lower latency, but may use additional ressources
> 
> Is this a "latency vs throughput" trade-off, or something more subtle?
> It would be nice to make the decision process as obvious as possible for
> the developer considering the use of this flag.


If you poll you can't do anything else, so you end up using CPU
cycles to wait which otherwise could do something productive.