Linux 4.1 compat: loop device on ZFS

Starting from Linux 4.1 allows iov_iter with bio_vec to be passed into
iter_read/iter_write. Notably, the loop device will pass bio_vec to backend
filesystem. However, current ZFS code assumes iovec without any check, so it
will always crash when using loop device.

With the restructured uio_t, we can safely pass bio_vec in uio_t with UIO_BVEC
set. The uio* functions are modified to handle bio_vec case separately.

The const uio_iov causes some warning in xuio related stuff, so explicit
convert them to non const.

Signed-off-by: Chunwei Chen <[email protected]>
Signed-off-by: Richard Yao <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Closes #3511
Closes #3640

1 files changed, 108 insertions, 97 deletions

diff --git a/module/zcommon/zfs_uio.c b/module/zcommon/zfs_uio.c
index 90376f2ac..a5634fca0 100644
--- a/module/zcommon/zfs_uio.c
+++ b/module/zcommon/zfs_uio.c
@@ -35,6 +35,9 @@
  * software developed by the University of California, Berkeley, and its
  * contributors.
  */
+/*
+ * Copyright (c) 2015 by Chunwei Chen. All rights reserved.
+ */
 
 /*
  * The uio support from OpenSolaris has been added as a short term
@@ -46,6 +49,7 @@
 
 #include <sys/types.h>
 #include <sys/uio_impl.h>
+#include <linux/kmap_compat.h>
 
 /*
  * Move "n" bytes at byte address "p"; "rw" indicates the direction
@@ -53,20 +57,17 @@
  * update to reflect the data which was moved.  Returns 0 on success or
  * a non-zero errno on failure.
  */
-int
-uiomove(void *p, size_t n, enum uio_rw rw, struct uio *uio)
+static int
+uiomove_iov(void *p, size_t n, enum uio_rw rw, struct uio *uio)
 {
-	struct iovec *iov;
+	const struct iovec *iov = uio->uio_iov;
+	size_t skip = uio->uio_skip;
 	ulong_t cnt;
 
+	ASSERT3U(skip, <, iov->iov_len);
+
 	while (n && uio->uio_resid) {
-		iov = uio->uio_iov;
-		cnt = MIN(iov->iov_len, n);
-		if (cnt == 0l) {
-			uio->uio_iov++;
-			uio->uio_iovcnt--;
-			continue;
-		}
+		cnt = MIN(iov->iov_len - skip, n);
 		switch (uio->uio_segflg) {
 		case UIO_USERSPACE:
 		case UIO_USERISPACE:
@@ -75,22 +76,29 @@ uiomove(void *p, size_t n, enum uio_rw rw, struct uio *uio)
 			 * iov->iov_base = user data pointer
 			 */
 			if (rw == UIO_READ) {
-				if (copy_to_user(iov->iov_base, p, cnt))
+				if (copy_to_user(iov->iov_base+skip, p, cnt))
 					return (EFAULT);
 			} else {
-				if (copy_from_user(p, iov->iov_base, cnt))
+				if (copy_from_user(p, iov->iov_base+skip, cnt))
 					return (EFAULT);
 			}
 			break;
 		case UIO_SYSSPACE:
 			if (rw == UIO_READ)
-				bcopy(p, iov->iov_base, cnt);
+				bcopy(p, iov->iov_base + skip, cnt);
 			else
-				bcopy(iov->iov_base, p, cnt);
+				bcopy(iov->iov_base + skip, p, cnt);
 			break;
+		default:
+			ASSERT(0);
+		}
+		skip += cnt;
+		if (skip == iov->iov_len) {
+			skip = 0;
+			uio->uio_iov = (++iov);
+			uio->uio_iovcnt--;
 		}
-		iov->iov_base += cnt;
-		iov->iov_len -= cnt;
+		uio->uio_skip = skip;
 		uio->uio_resid -= cnt;
 		uio->uio_loffset += cnt;
 		p = (caddr_t)p + cnt;
@@ -98,6 +106,50 @@ uiomove(void *p, size_t n, enum uio_rw rw, struct uio *uio)
 	}
 	return (0);
 }
+
+static int
+uiomove_bvec(void *p, size_t n, enum uio_rw rw, struct uio *uio)
+{
+	const struct bio_vec *bv = uio->uio_bvec;
+	size_t skip = uio->uio_skip;
+	ulong_t cnt;
+
+	ASSERT3U(skip, <, bv->bv_len);
+
+	while (n && uio->uio_resid) {
+		void *paddr;
+		cnt = MIN(bv->bv_len - skip, n);
+
+		paddr = zfs_kmap_atomic(bv->bv_page, KM_USER1);
+		if (rw == UIO_READ)
+			bcopy(p, paddr + bv->bv_offset + skip, cnt);
+		else
+			bcopy(paddr + bv->bv_offset + skip, p, cnt);
+		zfs_kunmap_atomic(paddr, KM_USER1);
+
+		skip += cnt;
+		if (skip == bv->bv_len) {
+			skip = 0;
+			uio->uio_bvec = (++bv);
+			uio->uio_iovcnt--;
+		}
+		uio->uio_skip = skip;
+		uio->uio_resid -= cnt;
+		uio->uio_loffset += cnt;
+		p = (caddr_t)p + cnt;
+		n -= cnt;
+	}
+	return (0);
+}
+
+int
+uiomove(void *p, size_t n, enum uio_rw rw, struct uio *uio)
+{
+	if (uio->uio_segflg != UIO_BVEC)
+		return (uiomove_iov(p, n, rw, uio));
+	else
+		return (uiomove_bvec(p, n, rw, uio));
+}
 EXPORT_SYMBOL(uiomove);
 
 #define	fuword8(uptr, vptr)	get_user((*vptr), (uptr))
@@ -111,39 +163,39 @@ EXPORT_SYMBOL(uiomove);
 void
 uio_prefaultpages(ssize_t n, struct uio *uio)
 {
-	struct iovec *iov;
+	const struct iovec *iov;
 	ulong_t cnt, incr;
 	caddr_t p;
 	uint8_t tmp;
 	int iovcnt;
+	size_t skip = uio->uio_skip;
+
+	/* no need to fault in kernel pages */
+	switch (uio->uio_segflg) {
+		case UIO_SYSSPACE:
+		case UIO_BVEC:
+			return;
+		case UIO_USERSPACE:
+		case UIO_USERISPACE:
+			break;
+		default:
+			ASSERT(0);
+	}
 
 	iov = uio->uio_iov;
 	iovcnt = uio->uio_iovcnt;
+	ASSERT3U(skip, <, iov->iov_len);
 
 	while ((n > 0) && (iovcnt > 0)) {
-		cnt = MIN(iov->iov_len, n);
-		if (cnt == 0) {
-			/* empty iov entry */
-			iov++;
-			iovcnt--;
-			continue;
-		}
+		cnt = MIN(iov->iov_len - skip, n);
 		n -= cnt;
 		/*
 		 * touch each page in this segment.
 		 */
-		p = iov->iov_base;
+		p = iov->iov_base + skip;
 		while (cnt) {
-			switch (uio->uio_segflg) {
-			case UIO_USERSPACE:
-			case UIO_USERISPACE:
-				if (fuword8((uint8_t *) p, &tmp))
-					return;
-				break;
-			case UIO_SYSSPACE:
-				bcopy(p, &tmp, 1);
-				break;
-			}
+			if (fuword8((uint8_t *) p, &tmp))
+				return;
 			incr = MIN(cnt, PAGESIZE);
 			p += incr;
 			cnt -= incr;
@@ -152,18 +204,11 @@ uio_prefaultpages(ssize_t n, struct uio *uio)
 		 * touch the last byte in case it straddles a page.
 		 */
 		p--;
-		switch (uio->uio_segflg) {
-		case UIO_USERSPACE:
-		case UIO_USERISPACE:
-			if (fuword8((uint8_t *) p, &tmp))
-				return;
-			break;
-		case UIO_SYSSPACE:
-			bcopy(p, &tmp, 1);
-			break;
-		}
+		if (fuword8((uint8_t *) p, &tmp))
+			return;
 		iov++;
 		iovcnt--;
+		skip = 0;
 	}
 }
 EXPORT_SYMBOL(uio_prefaultpages);
@@ -175,49 +220,13 @@ EXPORT_SYMBOL(uio_prefaultpages);
 int
 uiocopy(void *p, size_t n, enum uio_rw rw, struct uio *uio, size_t *cbytes)
 {
-	struct iovec *iov;
-	ulong_t cnt;
-	int iovcnt;
-
-	iovcnt = uio->uio_iovcnt;
-	*cbytes = 0;
-
-	for (iov = uio->uio_iov; n && iovcnt; iov++, iovcnt--) {
-		cnt = MIN(iov->iov_len, n);
-		if (cnt == 0)
-			continue;
-
-		switch (uio->uio_segflg) {
-
-		case UIO_USERSPACE:
-		case UIO_USERISPACE:
-			/*
-			 * p = kernel data pointer
-			 * iov->iov_base = user data pointer
-			 */
-			if (rw == UIO_READ) {
-				/* UIO_READ = copy data from kernel to user */
-				if (copy_to_user(iov->iov_base, p, cnt))
-					return (EFAULT);
-			} else {
-				/* UIO_WRITE = copy data from user to kernel */
-				if (copy_from_user(p, iov->iov_base, cnt))
-					return (EFAULT);
-			}
-			break;
+	struct uio uio_copy;
+	int ret;
 
-		case UIO_SYSSPACE:
-			if (rw == UIO_READ)
-				bcopy(p, iov->iov_base, cnt);
-			else
-				bcopy(iov->iov_base, p, cnt);
-			break;
-		}
-		p = (caddr_t)p + cnt;
-		n -= cnt;
-		*cbytes += cnt;
-	}
-	return (0);
+	bcopy(uio, &uio_copy, sizeof (struct uio));
+	ret = uiomove(p, n, rw, &uio_copy);
+	*cbytes = uio->uio_resid - uio_copy.uio_resid;
+	return (ret);
 }
 EXPORT_SYMBOL(uiocopy);
 
@@ -229,21 +238,23 @@ uioskip(uio_t *uiop, size_t n)
 {
 	if (n > uiop->uio_resid)
 		return;
-	while (n != 0) {
-		iovec_t	*iovp = uiop->uio_iov;
-		size_t		niovb = MIN(iovp->iov_len, n);
 
-		if (niovb == 0) {
+	uiop->uio_skip += n;
+	if (uiop->uio_segflg != UIO_BVEC) {
+		while (uiop->uio_skip >= uiop->uio_iov->iov_len) {
+			uiop->uio_skip -= uiop->uio_iov->iov_len;
 			uiop->uio_iov++;
 			uiop->uio_iovcnt--;
-			continue;
 		}
-		iovp->iov_base += niovb;
-		uiop->uio_loffset += niovb;
-		iovp->iov_len -= niovb;
-		uiop->uio_resid -= niovb;
-		n -= niovb;
+	} else {
+		while (uiop->uio_skip >= uiop->uio_bvec->bv_len) {
+			uiop->uio_skip -= uiop->uio_bvec->bv_len;
+			uiop->uio_bvec++;
+			uiop->uio_iovcnt--;
+		}
 	}
+	uiop->uio_loffset += n;
+	uiop->uio_resid -= n;
 }
 EXPORT_SYMBOL(uioskip);
 #endif /* _KERNEL */