Add kernel support for a Linux compatible copy_file_range(2) syscall.

This patch adds support to the kernel for a Linux compatible
copy_file_range(2) syscall and the related VOP_COPY_FILE_RANGE(9).
This syscall/VOP can be used by the NFSv4.2 client to implement the
Copy operation against an NFSv4.2 server to do file copies locally on
the server.
The vn_generic_copy_file_range() function in this patch can be used
by the NFSv4.2 server to implement the Copy operation.
Fuse may also me able to use the VOP_COPY_FILE_RANGE() method.

vn_generic_copy_file_range() attempts to maintain holes in the output
file in the range to be copied, but may fail to do so if the input and
output files are on different file systems with different _PC_MIN_HOLE_SIZE
values.

Separate commits will be done for the generated syscall files and userland
changes. A commit for a compat32 syscall will be done later.

Reviewed by:	kib, asomers (plus comments by brooks, jilles)
Relnotes:	yes
Differential Revision:	https://reviews.freebsd.org/D20584

7 files changed, 537 insertions, 0 deletions

diff --git a/sys/kern/syscalls.master b/sys/kern/syscalls.master
index f85c0ab3d2ff..879e2589c6bd 100644
--- a/sys/kern/syscalls.master
+++ b/sys/kern/syscalls.master
@@ -3175,6 +3175,16 @@
 		    int flag
 		);
 	}
+569	AUE_NULL	STD {
+		ssize_t copy_file_range(
+		    int infd,
+		    _Inout_opt_ off_t *inoffp,
+		    int outfd,
+		    _Inout_opt_ off_t *outoffp,
+		    size_t len,
+		    unsigned int flags
+		);
+	}
 
 ; Please copy any additions and changes to the following compatability tables:
 ; sys/compat/freebsd32/syscalls.master
diff --git a/sys/kern/vfs_default.c b/sys/kern/vfs_default.c
index 3c30d2e6c9f1..920d6f19c8a9 100644
--- a/sys/kern/vfs_default.c
+++ b/sys/kern/vfs_default.c
@@ -83,6 +83,7 @@ static int	dirent_exists(struct vnode *vp, const char *dirname,
 static int vop_stdis_text(struct vop_is_text_args *ap);
 static int vop_stdunset_text(struct vop_unset_text_args *ap);
 static int vop_stdadd_writecount(struct vop_add_writecount_args *ap);
+static int vop_stdcopy_file_range(struct vop_copy_file_range_args *ap);
 static int vop_stdfdatasync(struct vop_fdatasync_args *ap);
 static int vop_stdgetpages_async(struct vop_getpages_async_args *ap);
 
@@ -140,6 +141,7 @@ struct vop_vector default_vnodeops = {
 	.vop_set_text =		vop_stdset_text,
 	.vop_unset_text =	vop_stdunset_text,
 	.vop_add_writecount =	vop_stdadd_writecount,
+	.vop_copy_file_range =	vop_stdcopy_file_range,
 };
 
 /*
@@ -1212,6 +1214,17 @@ vfs_stdnosync (mp, waitfor)
 	return (0);
 }
 
+static int
+vop_stdcopy_file_range(struct vop_copy_file_range_args *ap)
+{
+	int error;
+
+	error = vn_generic_copy_file_range(ap->a_invp, ap->a_inoffp,
+	    ap->a_outvp, ap->a_outoffp, ap->a_lenp, ap->a_flags, ap->a_incred,
+	    ap->a_outcred, ap->a_fsizetd);
+	return (error);
+}
+
 int
 vfs_stdvget (mp, ino, flags, vpp)
 	struct mount *mp;
diff --git a/sys/kern/vfs_syscalls.c b/sys/kern/vfs_syscalls.c
index 5d9a59145d0e..ff0fc9f9867c 100644
--- a/sys/kern/vfs_syscalls.c
+++ b/sys/kern/vfs_syscalls.c
@@ -4814,3 +4814,122 @@ sys_posix_fadvise(struct thread *td, struct posix_fadvise_args *uap)
 	    uap->advice);
 	return (kern_posix_error(td, error));
 }
+
+int
+kern_copy_file_range(struct thread *td, int infd, off_t *inoffp, int outfd,
+    off_t *outoffp, size_t len, unsigned int flags)
+{
+	struct file *infp, *outfp;
+	struct vnode *invp, *outvp;
+	int error;
+	size_t retlen;
+	void *rl_rcookie, *rl_wcookie;
+	off_t savinoff, savoutoff;
+
+	infp = outfp = NULL;
+	rl_rcookie = rl_wcookie = NULL;
+	savinoff = -1;
+	error = 0;
+	retlen = 0;
+
+	if (flags != 0) {
+		error = EINVAL;
+		goto out;
+	}
+	if (len > SSIZE_MAX)
+		/*
+		 * Although the len argument is size_t, the return argument
+		 * is ssize_t (which is signed).  Therefore a size that won't
+		 * fit in ssize_t can't be returned.
+		 */
+		len = SSIZE_MAX;
+
+	/* Get the file structures for the file descriptors. */
+	error = fget_read(td, infd, &cap_read_rights, &infp);
+	if (error != 0)
+		goto out;
+	error = fget_write(td, outfd, &cap_write_rights, &outfp);
+	if (error != 0)
+		goto out;
+
+	/* Set the offset pointers to the correct place. */
+	if (inoffp == NULL)
+		inoffp = &infp->f_offset;
+	if (outoffp == NULL)
+		outoffp = &outfp->f_offset;
+	savinoff = *inoffp;
+	savoutoff = *outoffp;
+
+	invp = infp->f_vnode;
+	outvp = outfp->f_vnode;
+	/* Sanity check the f_flag bits. */
+	if ((outfp->f_flag & (FWRITE | FAPPEND)) != FWRITE ||
+	    (infp->f_flag & FREAD) == 0 || invp == outvp) {
+		error = EBADF;
+		goto out;
+	}
+
+	/* If len == 0, just return 0. */
+	if (len == 0)
+		goto out;
+
+	/* Range lock the byte ranges for both invp and outvp. */
+	for (;;) {
+		rl_wcookie = vn_rangelock_wlock(outvp, *outoffp, *outoffp +
+		    len);
+		rl_rcookie = vn_rangelock_tryrlock(invp, *inoffp, *inoffp +
+		    len);
+		if (rl_rcookie != NULL)
+			break;
+		vn_rangelock_unlock(outvp, rl_wcookie);
+		rl_rcookie = vn_rangelock_rlock(invp, *inoffp, *inoffp + len);
+		vn_rangelock_unlock(invp, rl_rcookie);
+	}
+
+	retlen = len;
+	error = vn_copy_file_range(invp, inoffp, outvp, outoffp, &retlen,
+	    flags, infp->f_cred, outfp->f_cred, td);
+out:
+	if (rl_rcookie != NULL)
+		vn_rangelock_unlock(invp, rl_rcookie);
+	if (rl_wcookie != NULL)
+		vn_rangelock_unlock(outvp, rl_wcookie);
+	if (savinoff != -1 && (error == EINTR || error == ERESTART)) {
+		*inoffp = savinoff;
+		*outoffp = savoutoff;
+	}
+	if (outfp != NULL)
+		fdrop(outfp, td);
+	if (infp != NULL)
+		fdrop(infp, td);
+	td->td_retval[0] = retlen;
+	return (error);
+}
+
+int
+sys_copy_file_range(struct thread *td, struct copy_file_range_args *uap)
+{
+	off_t inoff, outoff, *inoffp, *outoffp;
+	int error;
+
+	inoffp = outoffp = NULL;
+	if (uap->inoffp != NULL) {
+		error = copyin(uap->inoffp, &inoff, sizeof(off_t));
+		if (error != 0)
+			return (error);
+		inoffp = &inoff;
+	}
+	if (uap->outoffp != NULL) {
+		error = copyin(uap->outoffp, &outoff, sizeof(off_t));
+		if (error != 0)
+			return (error);
+		outoffp = &outoff;
+	}
+	error = kern_copy_file_range(td, uap->infd, inoffp, uap->outfd,
+	    outoffp, uap->len, uap->flags);
+	if (error == 0 && uap->inoffp != NULL)
+		error = copyout(inoffp, uap->inoffp, sizeof(off_t));
+	if (error == 0 && uap->outoffp != NULL)
+		error = copyout(outoffp, uap->outoffp, sizeof(off_t));
+	return (error);
+}
diff --git a/sys/kern/vfs_vnops.c b/sys/kern/vfs_vnops.c
index 4649848639dd..b6fe702d7b0a 100644
--- a/sys/kern/vfs_vnops.c
+++ b/sys/kern/vfs_vnops.c
@@ -2619,3 +2619,372 @@ loop2:
 
 	return (error);
 }
+
+/*
+ * Copies a byte range from invp to outvp.  Calls VOP_COPY_FILE_RANGE()
+ * or vn_generic_copy_file_range() after rangelocking the byte ranges,
+ * to do the actual copy.
+ * vn_generic_copy_file_range() is factored out, so it can be called
+ * from a VOP_COPY_FILE_RANGE() call as well, but handles vnodes from
+ * different file systems.
+ */
+int
+vn_copy_file_range(struct vnode *invp, off_t *inoffp, struct vnode *outvp,
+    off_t *outoffp, size_t *lenp, unsigned int flags, struct ucred *incred,
+    struct ucred *outcred, struct thread *fsize_td)
+{
+	struct vattr va;
+	int error;
+	size_t len;
+	uint64_t uvalin, uvalout;
+
+	len = *lenp;
+	*lenp = 0;		/* For error returns. */
+	error = 0;
+
+	/* Do some sanity checks on the arguments. */
+	uvalin = *inoffp;
+	uvalin += len;
+	uvalout = *outoffp;
+	uvalout += len;
+	if (invp->v_type == VDIR || outvp->v_type == VDIR)
+		error = EISDIR;
+	else if (*inoffp < 0 || uvalin > INT64_MAX || uvalin <
+	    (uint64_t)*inoffp || *outoffp < 0 || uvalout > INT64_MAX ||
+	    uvalout < (uint64_t)*outoffp || invp->v_type != VREG ||
+	    outvp->v_type != VREG)
+		error = EINVAL;
+	else if (invp == outvp)
+		error = EBADF;
+	if (error != 0)
+		goto out;
+
+	error = vn_lock(invp, LK_SHARED);
+	if (error != 0)
+		goto out;
+	/* Check that the offset + len does not go past EOF of invp. */
+	error = VOP_GETATTR(invp, &va, incred);
+	if (error == 0 && va.va_size < *inoffp + len)
+		error = EINVAL;
+	VOP_UNLOCK(invp, 0);
+	if (error != 0)
+		goto out;
+
+	/*
+	 * If the two vnode are for the same file system, call
+	 * VOP_COPY_FILE_RANGE(), otherwise call vn_generic_copy_file_range()
+	 * which can handle copies across multiple file systems.
+	 */
+	*lenp = len;
+	if (invp->v_mount == outvp->v_mount)
+		error = VOP_COPY_FILE_RANGE(invp, inoffp, outvp, outoffp,
+		    lenp, flags, incred, outcred, fsize_td);
+	else
+		error = vn_generic_copy_file_range(invp, inoffp, outvp,
+		    outoffp, lenp, flags, incred, outcred, fsize_td);
+out:
+	return (error);
+}
+
+/*
+ * Test len bytes of data starting at dat for all bytes == 0.
+ * Return true if all bytes are zero, false otherwise.
+ * Expects dat to be well aligned.
+ */
+static bool
+mem_iszero(void *dat, int len)
+{
+	int i;
+	const u_int *p;
+	const char *cp;
+
+	for (p = dat; len > 0; len -= sizeof(*p), p++) {
+		if (len >= sizeof(*p)) {
+			if (*p != 0)
+				return (false);
+		} else {
+			cp = (const char *)p;
+			for (i = 0; i < len; i++, cp++)
+				if (*cp != '\0')
+					return (false);
+		}
+	}
+	return (true);
+}
+
+/*
+ * Write an xfer sized chunk to outvp in blksize blocks from dat.
+ * dat is a maximum of blksize in length and can be written repeatedly in
+ * the chunk.
+ * If growfile == true, just grow the file via vn_truncate_locked() instead
+ * of doing actual writes.
+ */
+static int
+vn_write_outvp(struct vnode *outvp, char *dat, off_t outoff, off_t xfer,
+    u_long blksize, bool growfile, struct ucred *cred)
+{
+	struct mount *mp;
+	off_t xfer2;
+	int error, lckf;
+
+	/*
+	 * Loop around doing writes of blksize until write has been completed.
+	 * Lock/unlock on each loop iteration so that a bwillwrite() can be
+	 * done for each iteration, since the xfer argument can be very
+	 * large if there is a large hole to punch in the output file.
+	 */
+	do {
+		bwillwrite();
+		mp = NULL;
+		error = vn_start_write(outvp, &mp, V_WAIT);
+		if (error == 0) {
+			if (MNT_SHARED_WRITES(mp))
+				lckf = LK_SHARED;
+			else
+				lckf = LK_EXCLUSIVE;
+			error = vn_lock(outvp, lckf);
+		}
+		if (error == 0) {
+			if (growfile)
+				error = vn_truncate_locked(outvp, outoff + xfer,
+				    false, cred);
+			else {
+				xfer2 = MIN(xfer, blksize);
+				error = vn_rdwr(UIO_WRITE, outvp, dat, xfer2,
+				    outoff, UIO_SYSSPACE, IO_NODELOCKED,
+				    curthread->td_ucred, cred, NULL, curthread);
+				outoff += xfer2;
+				xfer -= xfer2;
+			}
+			VOP_UNLOCK(outvp, 0);
+		}
+		if (mp != NULL)
+			vn_finished_write(mp);
+	} while (!growfile && xfer > 0 && error == 0);
+	return (error);
+}
+
+/*
+ * Copy a byte range of one file to another.  This function can handle the
+ * case where invp and outvp are on different file systems.
+ * It can also be called by a VOP_COPY_FILE_RANGE() to do the work, if there
+ * is no better file system specific way to do it.
+ */
+int
+vn_generic_copy_file_range(struct vnode *invp, off_t *inoffp,
+    struct vnode *outvp, off_t *outoffp, size_t *lenp, unsigned int flags,
+    struct ucred *incred, struct ucred *outcred, struct thread *fsize_td)
+{
+	struct vattr va;
+	struct mount *mp;
+	struct uio io;
+	off_t startoff, endoff, xfer, xfer2;
+	u_long blksize;
+	int error;
+	bool cantseek, readzeros;
+	ssize_t aresid;
+	size_t copylen, len, savlen;
+	char *dat;
+	long holein, holeout;
+
+	holein = holeout = 0;
+	savlen = len = *lenp;
+	error = 0;
+	dat = NULL;
+
+	error = vn_lock(invp, LK_SHARED);
+	if (error != 0)
+		goto out;
+	if (VOP_PATHCONF(invp, _PC_MIN_HOLE_SIZE, &holein) != 0)
+		holein = 0;
+	VOP_UNLOCK(invp, 0);
+	if (error != 0)
+		goto out;
+
+	mp = NULL;
+	error = vn_start_write(outvp, &mp, V_WAIT);
+	if (error == 0)
+		error = vn_lock(outvp, LK_EXCLUSIVE);
+	if (error == 0) {
+		/*
+		 * If fsize_td != NULL, do a vn_rlimit_fsize() call,
+		 * now that outvp is locked.
+		 */
+		if (fsize_td != NULL) {
+			io.uio_offset = *outoffp;
+			io.uio_resid = len;
+			error = vn_rlimit_fsize(outvp, &io, fsize_td);
+			if (error != 0)
+				error = EFBIG;
+		}
+		if (VOP_PATHCONF(outvp, _PC_MIN_HOLE_SIZE, &holeout) != 0)
+			holeout = 0;
+		/*
+		 * Holes that are past EOF do not need to be written as a block
+		 * of zero bytes.  So, truncate the output file as far as
+		 * possible and then use va.va_size to decide if writing 0
+		 * bytes is necessary in the loop below.
+		 */
+		if (error == 0)
+			error = VOP_GETATTR(outvp, &va, outcred);
+		if (error == 0 && va.va_size > *outoffp && va.va_size <=
+		    *outoffp + len) {
+#ifdef MAC
+			error = mac_vnode_check_write(curthread->td_ucred,
+			    outcred, outvp);
+			if (error == 0)
+#endif
+				error = vn_truncate_locked(outvp, *outoffp,
+				    false, outcred);
+			if (error == 0)
+				va.va_size = *outoffp;
+		}
+		VOP_UNLOCK(outvp, 0);
+	}
+	if (mp != NULL)
+		vn_finished_write(mp);
+	if (error != 0)
+		goto out;
+
+	/*
+	 * Set the blksize to the larger of the hole sizes for invp and outvp.
+	 * If hole sizes aren't available, set the blksize to the larger 
+	 * f_iosize of invp and outvp.
+	 * This code expects the hole sizes and f_iosizes to be powers of 2.
+	 * This value is clipped at 4Kbytes and 1Mbyte.
+	 */
+	blksize = MAX(holein, holeout);
+	if (blksize == 0)
+		blksize = MAX(invp->v_mount->mnt_stat.f_iosize,
+		    outvp->v_mount->mnt_stat.f_iosize);
+	if (blksize < 4096)
+		blksize = 4096;
+	else if (blksize > 1024 * 1024)
+		blksize = 1024 * 1024;
+	dat = malloc(blksize, M_TEMP, M_WAITOK);
+
+	/*
+	 * If VOP_IOCTL(FIOSEEKHOLE) works for invp, use it and FIOSEEKDATA
+	 * to find holes.  Otherwise, just scan the read block for all 0s
+	 * in the inner loop where the data copying is done.
+	 * Note that some file systems such as NFSv3, NFSv4.0 and NFSv4.1 may
+	 * support holes on the server, but do not support FIOSEEKHOLE.
+	 */
+	while (len > 0 && error == 0) {
+		endoff = 0;			/* To shut up compilers. */
+		cantseek = true;
+		startoff = *inoffp;
+		copylen = len;
+
+		/*
+		 * Find the next data area.  If there is just a hole to EOF,
+		 * FIOSEEKDATA should fail and then we drop down into the
+		 * inner loop and create the hole on the outvp file.
+		 * (I do not know if any file system will report a hole to
+		 *  EOF via FIOSEEKHOLE, but I am pretty sure FIOSEEKDATA
+		 *  will fail for those file systems.)
+		 *
+		 * For input files that don't support FIOSEEKDATA/FIOSEEKHOLE,
+		 * the code just falls through to the inner copy loop.
+		 */
+		error = EINVAL;
+		if (holein > 0)
+			error = VOP_IOCTL(invp, FIOSEEKDATA, &startoff, 0,
+			    incred, curthread);
+		if (error == 0) {
+			endoff = startoff;
+			error = VOP_IOCTL(invp, FIOSEEKHOLE, &endoff, 0,
+			    incred, curthread);
+		}
+		if (error == 0) {
+			if (startoff > *inoffp) {
+				/* Found hole before data block. */
+				xfer = MIN(startoff - *inoffp, len);
+				if (*outoffp < va.va_size) {
+					/* Must write 0s to punch hole. */
+					xfer2 = MIN(va.va_size - *outoffp,
+					    xfer);
+					memset(dat, 0, MIN(xfer2, blksize));
+					error = vn_write_outvp(outvp, dat,
+					    *outoffp, xfer2, blksize, false,
+					    outcred);
+				}
+
+				if (error == 0 && *outoffp + xfer >
+				    va.va_size && xfer == len)
+					/* Grow last block. */
+					error = vn_write_outvp(outvp, dat,
+					    *outoffp, xfer, blksize, true,
+					    outcred);
+				if (error == 0) {
+					*inoffp += xfer;
+					*outoffp += xfer;
+					len -= xfer;
+				}
+			}
+			copylen = MIN(len, endoff - startoff);
+			cantseek = false;
+		} else {
+			cantseek = true;
+			startoff = *inoffp;
+			copylen = len;
+			error = 0;
+		}
+
+		xfer = blksize;
+		if (cantseek) {
+			/*
+			 * Set first xfer to end at a block boundary, so that
+			 * holes are more likely detected in the loop below via
+			 * the for all bytes 0 method.
+			 */
+			xfer -= (*inoffp % blksize);
+		}
+		/* Loop copying the data block. */
+		while (copylen > 0 && error == 0) {
+			if (copylen < xfer)
+				xfer = copylen;
+			error = vn_lock(invp, LK_SHARED);
+			if (error != 0)
+				goto out;
+			error = vn_rdwr(UIO_READ, invp, dat, xfer,
+			    startoff, UIO_SYSSPACE, IO_NODELOCKED,
+			    curthread->td_ucred, incred, &aresid,
+			    curthread);
+			VOP_UNLOCK(invp, 0);
+			/*
+			 * Linux considers a range that exceeds EOF to
+			 * be an error, so we will too.
+			 */
+			if (error == 0 && aresid > 0)
+				error = EINVAL;
+			if (error == 0) {
+				/*
+				 * Skip the write for holes past the initial EOF
+				 * of the output file, unless this is the last
+				 * write of the output file at EOF.
+				 */
+				readzeros = cantseek ? mem_iszero(dat, xfer) :
+				    false;
+				if (!cantseek || *outoffp < va.va_size ||
+				    xfer == len || !readzeros)
+					error = vn_write_outvp(outvp, dat,
+					    *outoffp, xfer, blksize,
+					    readzeros && xfer == len &&
+					    *outoffp >= va.va_size, outcred);
+				if (error == 0) {
+					*inoffp += xfer;
+					startoff += xfer;
+					*outoffp += xfer;
+					copylen -= xfer;
+					len -= xfer;
+				}
+			}
+			xfer = blksize;
+		}
+	}
+out:
+	*lenp = savlen - len;
+	free(dat, M_TEMP);
+	return (error);
+}
diff --git a/sys/kern/vnode_if.src b/sys/kern/vnode_if.src
index 68fa84079af6..dc0c08424ca9 100644
--- a/sys/kern/vnode_if.src
+++ b/sys/kern/vnode_if.src
@@ -718,6 +718,22 @@ vop_fdatasync {
 };
 
 
+%% copy_file_range	invp	U U U
+%% copy_file_range	outvp	U U U
+
+vop_copy_file_range {
+	IN struct vnode *invp;
+	INOUT off_t *inoffp;
+	IN struct vnode *outvp;
+	INOUT off_t *outoffp;
+	INOUT size_t *lenp;
+	IN unsigned int flags;
+	IN struct ucred *incred;
+	IN struct ucred *outcred;
+	IN struct thread *fsizetd;
+};
+
+
 # The VOPs below are spares at the end of the table to allow new VOPs to be
 # added in stable branches without breaking the KBI.  New VOPs in HEAD should
 # be added above these spares.  When merging a new VOP to a stable branch,
diff --git a/sys/sys/syscallsubr.h b/sys/sys/syscallsubr.h
index 0c3ec79071d8..beb6e503ebc7 100644
--- a/sys/sys/syscallsubr.h
+++ b/sys/sys/syscallsubr.h
@@ -94,6 +94,8 @@ int	kern_clock_settime(struct thread *td, clockid_t clock_id,
 int	kern_close(struct thread *td, int fd);
 int	kern_connectat(struct thread *td, int dirfd, int fd,
 	    struct sockaddr *sa);
+int	kern_copy_file_range(struct thread *td, int infd, off_t *inoffp,
+	    int outfd, off_t *outoffp, size_t len, unsigned int flags);
 int	kern_cpuset_getaffinity(struct thread *td, cpulevel_t level,
 	    cpuwhich_t which, id_t id, size_t cpusetsize, cpuset_t *maskp);
 int	kern_cpuset_setaffinity(struct thread *td, cpulevel_t level,
diff --git a/sys/sys/vnode.h b/sys/sys/vnode.h
index 92615c781bb0..faf1f1ac477a 100644
--- a/sys/sys/vnode.h
+++ b/sys/sys/vnode.h
@@ -667,9 +667,17 @@ int	vn_bmap_seekhole(struct vnode *vp, u_long cmd, off_t *off,
 	    struct ucred *cred);
 int	vn_close(struct vnode *vp,
 	    int flags, struct ucred *file_cred, struct thread *td);
+int	vn_copy_file_range(struct vnode *invp, off_t *inoffp,
+	    struct vnode *outvp, off_t *outoffp, size_t *lenp,
+	    unsigned int flags, struct ucred *incred, struct ucred *outcred,
+	    struct thread *fsize_td);
 void	vn_finished_write(struct mount *mp);
 void	vn_finished_secondary_write(struct mount *mp);
 int	vn_fsync_buf(struct vnode *vp, int waitfor);
+int	vn_generic_copy_file_range(struct vnode *invp, off_t *inoffp,
+	    struct vnode *outvp, off_t *outoffp, size_t *lenp,
+	    unsigned int flags, struct ucred *incred, struct ucred *outcred,
+	    struct thread *fsize_td);
 int	vn_isdisk(struct vnode *vp, int *errp);
 int	_vn_lock(struct vnode *vp, int flags, char *file, int line);
 #define vn_lock(vp, flags) _vn_lock(vp, flags, __FILE__, __LINE__)