Linux 4.1 compat: use read_iter() / write_iter()

Linux 3.15 commit torvalds/linux@293bc98 introduced two new methods.
The ->read_iter() and ->write_iter() methods were designed to replace
the ->aio_read() and ->aio_write() interfaces.  Both interfaces were
preserved for several kernel releases in order to migrate all existing
consumers to the new interfaces.  But as of Linux 4.1 the legacy
interface has been retired and the ZFS code must be updated to use
the new interfaces.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #3352

config/kernel-vfs-rw-iterate.m4

@@ -0,0 +1,27 @@
+dnl #
+dnl # Linux 4.1.x API
+dnl #
+AC_DEFUN([ZFS_AC_KERNEL_VFS_RW_ITERATE],
+	[AC_MSG_CHECKING([whether fops->read/write_iter() are available])
+	ZFS_LINUX_TRY_COMPILE([
+		#include <linux/fs.h>
+
+		ssize_t test_read(struct kiocb *kiocb, struct iov_iter *to)
+		    { return 0; }
+		ssize_t test_write(struct kiocb *kiocb, struct iov_iter *from)
+		    { return 0; }
+
+		static const struct file_operations
+		    fops __attribute__ ((unused)) = {
+		    .read_iter = test_read,
+		    .write_iter = test_write,
+		};
+	],[
+	],[
+		AC_MSG_RESULT(yes)
+		AC_DEFINE(HAVE_VFS_RW_ITERATE, 1,
+			[fops->read/write_iter() are available])
+	],[
+		AC_MSG_RESULT(no)
+	])
+])

config/kernel.m4

@@ -96,6 +96,7 @@ AC_DEFUN([ZFS_AC_CONFIG_KERNEL], [
 	ZFS_AC_KERNEL_5ARG_SGET
 	ZFS_AC_KERNEL_LSEEK_EXECUTE
 	ZFS_AC_KERNEL_VFS_ITERATE
+	ZFS_AC_KERNEL_VFS_RW_ITERATE
 
 	AS_IF([test "$LINUX_OBJ" != "$LINUX"], [
 		KERNELMAKE_PARAMS="$KERNELMAKE_PARAMS O=$LINUX_OBJ"

module/zfs/zpl_file.c

@@ -196,8 +196,7 @@ zpl_fsync(struct file *filp, loff_t start, loff_t end, int datasync)
 static int
 zpl_aio_fsync(struct kiocb *kiocb, int datasync)
 {
-	return (zpl_fsync(kiocb->ki_filp, kiocb->ki_pos,
-	    kiocb->ki_pos + kiocb->ki_nbytes, datasync));
+	return (zpl_fsync(kiocb->ki_filp, kiocb->ki_pos, -1, datasync));
 }
 #else
 #error "Unsupported fops->fsync() implementation"
@@ -261,12 +260,11 @@ zpl_read(struct file *filp, char __user *buf, size_t len, loff_t *ppos)
 }
 
 static ssize_t
-zpl_aio_read(struct kiocb *kiocb, const struct iovec *iovp,
-	unsigned long nr_segs, loff_t pos)
+zpl_iter_read_common(struct kiocb *kiocb, const struct iovec *iovp,
+    unsigned long nr_segs, size_t count)
 {
 	cred_t *cr = CRED();
 	struct file *filp = kiocb->ki_filp;
-	size_t count = kiocb->ki_nbytes;
 	ssize_t read;
 	size_t alloc_size = sizeof (struct iovec) * nr_segs;
 	struct iovec *iov_tmp = kmem_alloc(alloc_size, KM_SLEEP);
@@ -284,6 +282,22 @@ zpl_aio_read(struct kiocb *kiocb, const struct iovec *iovp,
 	return (read);
 }
 
+#if defined(HAVE_VFS_RW_ITERATE)
+static ssize_t
+zpl_iter_read(struct kiocb *kiocb, struct iov_iter *to)
+{
+	return (zpl_iter_read_common(kiocb, to->iov, to->nr_segs,
+	    iov_iter_count(to)));
+}
+#else
+static ssize_t
+zpl_aio_read(struct kiocb *kiocb, const struct iovec *iovp,
+    unsigned long nr_segs, loff_t pos)
+{
+	return (zpl_iter_read_common(kiocb, iovp, nr_segs, kiocb->ki_nbytes));
+}
+#endif /* HAVE_VFS_RW_ITERATE */
+
 static inline ssize_t
 zpl_write_common_iovec(struct inode *ip, const struct iovec *iovp, size_t count,
     unsigned long nr_segs, loff_t *ppos, uio_seg_t segment,
@@ -344,12 +358,11 @@ zpl_write(struct file *filp, const char __user *buf, size_t len, loff_t *ppos)
 }
 
 static ssize_t
-zpl_aio_write(struct kiocb *kiocb, const struct iovec *iovp,
-	unsigned long nr_segs, loff_t pos)
+zpl_iter_write_common(struct kiocb *kiocb, const struct iovec *iovp,
+    unsigned long nr_segs, size_t count)
 {
 	cred_t *cr = CRED();
 	struct file *filp = kiocb->ki_filp;
-	size_t count = kiocb->ki_nbytes;
 	ssize_t wrote;
 	size_t alloc_size = sizeof (struct iovec) * nr_segs;
 	struct iovec *iov_tmp = kmem_alloc(alloc_size, KM_SLEEP);
@@ -367,6 +380,22 @@ zpl_aio_write(struct kiocb *kiocb, const struct iovec *iovp,
 	return (wrote);
 }
 
+#if defined(HAVE_VFS_RW_ITERATE)
+static ssize_t
+zpl_iter_write(struct kiocb *kiocb, struct iov_iter *from)
+{
+	return (zpl_iter_write_common(kiocb, from->iov, from->nr_segs,
+	    iov_iter_count(from)));
+}
+#else
+static ssize_t
+zpl_aio_write(struct kiocb *kiocb, const struct iovec *iovp,
+    unsigned long nr_segs, loff_t pos)
+{
+	return (zpl_iter_write_common(kiocb, iovp, nr_segs, kiocb->ki_nbytes));
+}
+#endif /* HAVE_VFS_RW_ITERATE */
+
 static loff_t
 zpl_llseek(struct file *filp, loff_t offset, int whence)
 {
@@ -778,8 +807,13 @@ const struct file_operations zpl_file_operations = {
 	.llseek		= zpl_llseek,
 	.read		= zpl_read,
 	.write		= zpl_write,
+#ifdef HAVE_VFS_RW_ITERATE
+	.read_iter	= zpl_iter_read,
+	.write_iter	= zpl_iter_write,
+#else
 	.aio_read	= zpl_aio_read,
 	.aio_write	= zpl_aio_write,
+#endif
 	.mmap		= zpl_mmap,
 	.fsync		= zpl_fsync,
 	.aio_fsync	= zpl_aio_fsync,