[PATCH 0/4] vfs: Non-blockling buffered fs read (page cache only)

@@ -350,9 +350,9 @@ static int fd_do_rw(struct se_cmd *cmd, struct scatterlist *sgl,
 	set_fs(get_ds());
 
 	if (is_write)
-		ret = vfs_writev(fd, &iov[0], sgl_nents, &pos);
+		ret = vfs_writev(fd, &iov[0], sgl_nents, &pos, 0);
 	else
-		ret = vfs_readv(fd, &iov[0], sgl_nents, &pos);
+		ret = vfs_readv(fd, &iov[0], sgl_nents, &pos, 0);
 
 	set_fs(old_fs);
 

@@ -528,7 +528,7 @@ fd_execute_write_same(struct se_cmd *cmd)
 
 	old_fs = get_fs();
 	set_fs(get_ds());
-	rc = vfs_writev(f, &iov[0], iov_num, &pos);
+	rc = vfs_writev(f, &iov[0], iov_num, &pos, 0);
 	set_fs(old_fs);
 
 	vfree(iov);

@@ -872,7 +872,7 @@ __be32 nfsd_readv(struct file *file, loff_t offset, struct kvec *vec, int vlen,
 
 	oldfs = get_fs();
 	set_fs(KERNEL_DS);
-	host_err = vfs_readv(file, (struct iovec __user *)vec, vlen, &offset);
+	host_err = vfs_readv(file, (struct iovec __user *)vec, vlen, &offset, 0);
 	set_fs(oldfs);
 	return nfsd_finish_read(file, count, host_err);
 }

@@ -960,7 +960,7 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp, struct file *file,
 
 	/* Write the data. */
 	oldfs = get_fs(); set_fs(KERNEL_DS);
-	host_err = vfs_writev(file, (struct iovec __user *)vec, vlen, &pos);
+	host_err = vfs_writev(file, (struct iovec __user *)vec, vlen, &pos, 0);
 	set_fs(oldfs);
 	if (host_err < 0)
 		goto out_nfserr;

@@ -653,7 +653,8 @@ unsigned long iov_shorten(struct iovec *iov, unsigned long nr_segs, size_t to)
 EXPORT_SYMBOL(iov_shorten);
 
 static ssize_t do_iter_readv_writev(struct file *filp, int rw, const struct iovec *iov,
-		unsigned long nr_segs, size_t len, loff_t *ppos, iter_fn_t fn)
+		unsigned long nr_segs, size_t len, loff_t *ppos, iter_fn_t fn,
+		int flags)
 {
 	struct kiocb kiocb;
 	struct iov_iter iter;

@@ -662,6 +663,7 @@ static ssize_t do_iter_readv_writev(struct file *filp, int rw, const struct iove
 	init_sync_kiocb(&kiocb, filp);
 	kiocb.ki_pos = *ppos;
 	kiocb.ki_nbytes = len;
+	kiocb.ki_rwflags = flags;
 
 	iov_iter_init(&iter, rw, iov, nr_segs, len);
 	ret = fn(&kiocb, &iter);

@@ -800,7 +802,8 @@ out:
 
 static ssize_t do_readv_writev(int type, struct file *file,
 			       const struct iovec __user * uvector,
-			       unsigned long nr_segs, loff_t *pos)
+			       unsigned long nr_segs, loff_t *pos,
+			       int flags)
 {
 	size_t tot_len;
 	struct iovec iovstack[UIO_FASTIOV];

@@ -834,7 +837,7 @@ static ssize_t do_readv_writev(int type, struct file *file,
 
 	if (iter_fn)
 		ret = do_iter_readv_writev(file, type, iov, nr_segs, tot_len,
-						pos, iter_fn);
+						pos, iter_fn, flags);
 	else if (fnv)
 		ret = do_sync_readv_writev(file, iov, nr_segs, tot_len,
 						pos, fnv);

@@ -857,27 +860,27 @@ out:
 }
 
 ssize_t vfs_readv(struct file *file, const struct iovec __user *vec,
-		  unsigned long vlen, loff_t *pos)
+		  unsigned long vlen, loff_t *pos, int flags)
 {
 	if (!(file->f_mode & FMODE_READ))
 		return -EBADF;
 	if (!(file->f_mode & FMODE_CAN_READ))
 		return -EINVAL;
 
-	return do_readv_writev(READ, file, vec, vlen, pos);
+	return do_readv_writev(READ, file, vec, vlen, pos, flags);
 }
 
 EXPORT_SYMBOL(vfs_readv);
 
 ssize_t vfs_writev(struct file *file, const struct iovec __user *vec,
-		   unsigned long vlen, loff_t *pos)
+		   unsigned long vlen, loff_t *pos, int flags)
 {
 	if (!(file->f_mode & FMODE_WRITE))
 		return -EBADF;
 	if (!(file->f_mode & FMODE_CAN_WRITE))
 		return -EINVAL;
 
-	return do_readv_writev(WRITE, file, vec, vlen, pos);
+	return do_readv_writev(WRITE, file, vec, vlen, pos, flags);
 }
 
 EXPORT_SYMBOL(vfs_writev);

@@ -890,7 +893,7 @@ SYSCALL_DEFINE3(readv, unsigned long, fd, const struct iovec __user *, vec,
 
 	if (f.file) {
 		loff_t pos = file_pos_read(f.file);
-		ret = vfs_readv(f.file, vec, vlen, &pos);
+		ret = vfs_readv(f.file, vec, vlen, &pos, 0);
 		if (ret >= 0)
 			file_pos_write(f.file, pos);
 		fdput_pos(f);

@@ -910,7 +913,7 @@ SYSCALL_DEFINE3(writev, unsigned long, fd, const struct iovec __user *, vec,
 
 	if (f.file) {
 		loff_t pos = file_pos_read(f.file);
-		ret = vfs_writev(f.file, vec, vlen, &pos);
+		ret = vfs_writev(f.file, vec, vlen, &pos, 0);
 		if (ret >= 0)
 			file_pos_write(f.file, pos);
 		fdput_pos(f);

@@ -942,7 +945,7 @@ 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);
+			ret = vfs_readv(f.file, vec, vlen, &pos, 0);
 		fdput(f);
 	}
 

@@ -966,7 +969,7 @@ 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);
+			ret = vfs_writev(f.file, vec, vlen, &pos, 0);
 		fdput(f);
 	}
 

@@ -1014,7 +1017,7 @@ static ssize_t compat_do_readv_writev(int type, struct file *file,
 
 	if (iter_fn)
 		ret = do_iter_readv_writev(file, type, iov, nr_segs, tot_len,
-						pos, iter_fn);
+						pos, iter_fn, 0);
 	else if (fnv)
 		ret = do_sync_readv_writev(file, iov, nr_segs, tot_len,
 						pos, fnv);

@@ -1113,6 +1116,7 @@ COMPAT_SYSCALL_DEFINE5(preadv, compat_ulong_t, fd,
 	return __compat_sys_preadv64(fd, vec, vlen, pos);
 }
 
+
 static size_t compat_writev(struct file *file,
 			    const struct compat_iovec __user *vec,
 			    unsigned long vlen, loff_t *pos)

@@ -576,7 +576,7 @@ static ssize_t kernel_readv(struct file *file, const struct iovec *vec,
 	old_fs = get_fs();
 	set_fs(get_ds());
 	/* The cast to a user pointer is valid due to the set_fs() */
-	res = vfs_readv(file, (const struct iovec __user *)vec, vlen, &pos);
+	res = vfs_readv(file, (const struct iovec __user *)vec, vlen, &pos, 0);
 	set_fs(old_fs);
 
 	return res;

@@ -52,6 +52,8 @@ struct kiocb {
 	 * this is the underlying eventfd context to deliver events to.
 	 */
 	struct eventfd_ctx	*ki_eventfd;
+
+	int			ki_rwflags;
 };
 
 static inline bool is_sync_kiocb(struct kiocb *kiocb)

@@ -1538,9 +1538,9 @@ ssize_t rw_copy_check_uvector(int type, const struct iovec __user * uvector,
 extern ssize_t vfs_read(struct file *, char __user *, size_t, loff_t *);
 extern ssize_t vfs_write(struct file *, const char __user *, size_t, loff_t *);
 extern ssize_t vfs_readv(struct file *, const struct iovec __user *,
-		unsigned long, loff_t *);
+		unsigned long, loff_t *, int);
 extern ssize_t vfs_writev(struct file *, const struct iovec __user *,
-		unsigned long, loff_t *);
+		unsigned long, loff_t *, int);
 
 struct super_operations {
    	struct inode *(*alloc_inode)(struct super_block *sb);

@@ -1465,7 +1465,7 @@ static void shrink_readahead_size_eio(struct file *filp,
  * of the logic when it comes to error handling etc.
  */
 static ssize_t do_generic_file_read(struct file *filp, loff_t *ppos,
-		struct iov_iter *iter, ssize_t written)
+		struct iov_iter *iter, ssize_t written, int flags)
 {
 	struct address_space *mapping = filp->f_mapping;
 	struct inode *inode = mapping->host;

@@ -866,6 +866,8 @@ ssize_t vfs_readv(struct file *file, const struct iovec __user *vec,
 		return -EBADF;
 	if (!(file->f_mode & FMODE_CAN_READ))
 		return -EINVAL;
+	if (flags & ~0)
+		return -EINVAL;
 
 	return do_readv_writev(READ, file, vec, vlen, pos, flags);
 }

@@ -879,21 +881,23 @@ ssize_t vfs_writev(struct file *file, const struct iovec __user *vec,
 		return -EBADF;
 	if (!(file->f_mode & FMODE_CAN_WRITE))
 		return -EINVAL;
+	if (flags & ~0)
+		return -EINVAL;
 
 	return do_readv_writev(WRITE, file, vec, vlen, pos, flags);
 }
 
 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);

@@ -905,15 +909,15 @@ 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);

@@ -931,10 +935,9 @@ 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;
 

@@ -945,7 +948,7 @@ 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);
 	}
 

@@ -955,10 +958,9 @@ 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;
 

@@ -969,7 +971,7 @@ 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);
 	}
 

@@ -979,6 +981,58 @@ 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,

@@ -571,8 +571,14 @@ 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);

@@ -213,6 +213,10 @@ __SC_COMP(__NR_pwrite64, sys_pwrite64, compat_sys_pwrite64)
 __SC_COMP(__NR_preadv, sys_preadv, compat_sys_preadv)
 #define __NR_pwritev 70
 __SC_COMP(__NR_pwritev, sys_pwritev, compat_sys_pwritev)
+#define __NR_preadv2 281
+__SC_COMP(__NR_preadv2, sys_preadv2)
+#define __NR_pwritev2 282
+__SC_COMP(__NR_pwritev2, sys_pwritev2)
 
 /* fs/sendfile.c */
 #define __NR3264_sendfile 71

@@ -709,7 +713,7 @@ __SYSCALL(__NR_memfd_create, sys_memfd_create)
 __SYSCALL(__NR_bpf, sys_bpf)
 
 #undef __NR_syscalls
-#define __NR_syscalls 281
+#define __NR_syscalls 283
 
 /*
  * All syscalls below here should go away really,

@@ -1735,7 +1735,7 @@ generic_file_read_iter(struct kiocb *iocb, struct iov_iter *iter)
 		}
 	}
 
-	retval = do_generic_file_read(file, ppos, iter, retval);
+	retval = do_generic_file_read(file, ppos, iter, retval, iocb->ki_rwflags);
 out:
 	return retval;
 }

@@ -364,3 +364,5 @@
 355	i386	getrandom		sys_getrandom
 356	i386	memfd_create		sys_memfd_create
 357	i386	bpf			sys_bpf
+358	i386	preadv2			sys_preadv2
+359	i386	pwritev2		sys_pwritev2

@@ -328,6 +328,8 @@
 319	common	memfd_create		sys_memfd_create
 320	common	kexec_file_load		sys_kexec_file_load
 321	common	bpf			sys_bpf
+322	64	preadv2			sys_preadv2
+323	64	pwritev2		sys_pwritev2
 
 #
 # x32-specific system call numbers start at 512 to avoid cache impact

@@ -3005,6 +3005,9 @@ ssize_t cifs_user_readv(struct kiocb *iocb, struct iov_iter *to)
 	struct cifs_readdata *rdata, *tmp;
 	struct list_head rdata_list;
 
+	if (iocb->ki_rwflags & RWF_NONBLOCK)
+		return -EAGAIN;
+
 	len = iov_iter_count(to);
 	if (!len)
 		return 0;

@@ -3123,6 +3126,9 @@ cifs_strict_readv(struct kiocb *iocb, struct iov_iter *to)
 	    ((cifs_sb->mnt_cifs_flags & CIFS_MOUNT_NOPOSIXBRL) == 0))
 		return generic_file_read_iter(iocb, to);
 
+	if (iocb->ki_rwflags & RWF_NONBLOCK)
+		return -EAGAIN;
+
 	/*
 	 * We need to hold the sem to be sure nobody modifies lock list
 	 * with a brlock that prevents reading.

@@ -2472,6 +2472,12 @@ static ssize_t ocfs2_file_read_iter(struct kiocb *iocb,
 			filp->f_path.dentry->d_name.name,
 			to->nr_segs);	/* GRRRRR */
 
+	/*
+	 * No non-blocking reads for ocfs2 for now.  Might be doable with
+	 * non-blocking cluster lock helpers.
+	 */
+	if (iocb->ki_rwflags & RWF_NONBLOCK)
+		return -EAGAIN;
 
 	if (!inode) {
 		ret = -EINVAL;

@@ -302,7 +302,8 @@ pipe_read(struct kiocb *iocb, struct iov_iter *to)
 			 */
 			if (ret)
 				break;
-			if (filp->f_flags & O_NONBLOCK) {
+			if ((filp->f_flags & O_NONBLOCK) ||
+			    (iocb->ki_rwflags & RWF_NONBLOCK)) {
 				ret = -EAGAIN;
 				break;
 			}

@@ -835,14 +835,19 @@ static ssize_t do_readv_writev(int type, struct file *file,
 		file_start_write(file);
 	}
 
-	if (iter_fn)
+	if (iter_fn) {
 		ret = do_iter_readv_writev(file, type, iov, nr_segs, tot_len,
 						pos, iter_fn, flags);
-	else if (fnv)
-		ret = do_sync_readv_writev(file, iov, nr_segs, tot_len,
-						pos, fnv);
-	else
-		ret = do_loop_readv_writev(file, iov, nr_segs, pos, fn);
+	} else {
+		if (type == READ && (flags & RWF_NONBLOCK))
+			return -EAGAIN;
+
+		if (fnv)
+			ret = do_sync_readv_writev(file, iov, nr_segs, tot_len,
+							pos, fnv);
+		else
+			ret = do_loop_readv_writev(file, iov, nr_segs, pos, fn);
+	}
 
 	if (type != READ)
 		file_end_write(file);

@@ -866,8 +871,10 @@ ssize_t vfs_readv(struct file *file, const struct iovec __user *vec,
 		return -EBADF;
 	if (!(file->f_mode & FMODE_CAN_READ))
 		return -EINVAL;
-	if (flags & ~0)
+	if (flags & ~RWF_NONBLOCK)
 		return -EINVAL;
+	if ((file->f_flags & O_DIRECT) && (flags & RWF_NONBLOCK))
+		return -EAGAIN;
 
 	return do_readv_writev(READ, file, vec, vlen, pos, flags);
 }

@@ -246,6 +246,10 @@ xfs_file_read_iter(
 
 	XFS_STATS_INC(xs_read_calls);
 
+	/* XXX: need a non-blocking iolock helper, shouldn't be too hard */
+	if (iocb->ki_rwflags & RWF_NONBLOCK)
+		return -EAGAIN;
+
 	if (unlikely(file->f_flags & O_DIRECT))
 		ioflags |= XFS_IO_ISDIRECT;
 	if (file->f_mode & FMODE_NOCMTIME)

@@ -1459,6 +1459,9 @@ struct block_device_operations;
 #define HAVE_COMPAT_IOCTL 1
 #define HAVE_UNLOCKED_IOCTL 1
 
+/* These flags are used for the readv/writev syscalls with flags. */
+#define RWF_NONBLOCK 0x00000001
+
 struct iov_iter;
 
 struct file_operations {

@@ -1493,6 +1493,8 @@ static ssize_t do_generic_file_read(struct file *filp, loff_t *ppos,
 find_page:
 		page = find_get_page(mapping, index);
 		if (!page) {
+			if (flags & RWF_NONBLOCK)
+				goto would_block;
 			page_cache_sync_readahead(mapping,
 					ra, filp,
 					index, last_index - index);

@@ -1584,6 +1586,11 @@ page_ok:
 		continue;
 
 page_not_up_to_date:
+		if (flags & RWF_NONBLOCK) {
+			page_cache_release(page);
+			goto would_block;
+		}
+
 		/* Get exclusive access to the page ... */
 		error = lock_page_killable(page);
 		if (unlikely(error))

@@ -1603,6 +1610,12 @@ page_not_up_to_date_locked:
 			goto page_ok;
 		}
 
+		if (flags & RWF_NONBLOCK) {
+			unlock_page(page);
+			page_cache_release(page);
+			goto would_block;
+		}
+
 readpage:
 		/*
 		 * A previous I/O error may have been due to temporary

@@ -1673,6 +1686,8 @@ no_cached_page:
 		goto readpage;
 	}
 
+would_block:
+	error = -EAGAIN;
 out:
 	ra->prev_pos = prev_index;
 	ra->prev_pos <<= PAGE_CACHE_SHIFT;

@@ -1706,6 +1721,9 @@ generic_file_read_iter(struct kiocb *iocb, struct iov_iter *iter)
 		size_t count = iov_iter_count(iter);
 		loff_t size;
 
+		if (iocb->ki_rwflags & RWF_NONBLOCK)
+			return -EAGAIN;
+
 		if (!count)
 			goto out; /* skip atime */
 		size = i_size_read(inode);

@@ -1531,6 +1531,10 @@ static ssize_t shmem_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
 	ssize_t retval = 0;
 	loff_t *ppos = &iocb->ki_pos;
 
+	/* XXX: should be easily supportable */
+	if (iocb->ki_rwflags & RWF_NONBLOCK)
+		return -EAGAIN;
+
 	/*
 	 * Might this read be for a stacking filesystem?  Then when reading
 	 * holes of a sparse file, we actually need to allocate those pages,

@@ -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

@@ -162,9 +168,9 @@ 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

@@ -174,15 +180,41 @@ 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_NONBLOCK " (only " preadv2() " since Linux 3.19)"
+Performs a non-blocking operation for regular files (not sockets) opened in buffered mode (not
+.BR O_DIRECT ")."
+
 .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.
 On error, \-1 is returned, and \fIerrno\fP is set appropriately.
 .SH ERRORS

@@ -191,12 +223,22 @@ 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:
+Additionally, the following errors are defined:
+.TP
+.B EAGAIN
+The operation would block. This is possible if the file descriptor \fIfd\fP refers to a socket and has been marked nonblocking
+.RB ( O_NONBLOCK ),
+or the operation is a
+.BR preadv2
+and the \fIflags\fP argument is set to
+.BR RWF_NONBLOCK.
 .TP
 .B EINVAL
 The sum of the

@@ -205,12 +247,17 @@ values overflows an
 .I ssize_t
 value.
 Or, 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 3.19 (if we're lucky);
 .SH CONFORMING TO
 .BR readv (),
 .BR writev ():

@@ -223,6 +270,10 @@ first appeared in Linux 2.6.30; library support was added in glibc 2.10.
 .BR preadv (),
 .BR pwritev ():
 nonstandard, but present also on the modern BSDs.
+.sp
+.BR preadv2 (),
+.BR pwritev2 ():
+nonstandard, Linux extension.
 .SH NOTES
 .SS C library/kernel ABI differences
 POSIX.1-2001 allows an implementation to place a limit on