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From: John Baldwin <jhb@FreeBSD.org>
Date: Wed, 3 Mar 2010 16:18:05 +0000 (UTC)
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Subject: svn commit: r204638 - head/sys/kern
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Author: jhb
Date: Wed Mar  3 16:18:04 2010
New Revision: 204638
URL: http://svn.freebsd.org/changeset/base/204638

Log:
  Allow lseek(SEEK_END) to work on disk devices by using the DIOCGMEDIASIZE
  to determine the media size.
  
  Submitted by:	nox
  MFC after:	1 week

Modified:
  head/sys/kern/vfs_syscalls.c

Modified: head/sys/kern/vfs_syscalls.c
==============================================================================
--- head/sys/kern/vfs_syscalls.c	Wed Mar  3 16:06:43 2010	(r204637)
+++ head/sys/kern/vfs_syscalls.c	Wed Mar  3 16:18:04 2010	(r204638)
@@ -45,6 +45,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/systm.h>
 #include <sys/bio.h>
 #include <sys/buf.h>
+#include <sys/disk.h>
 #include <sys/sysent.h>
 #include <sys/malloc.h>
 #include <sys/mount.h>
@@ -1920,7 +1921,7 @@ lseek(td, uap)
 	struct file *fp;
 	struct vnode *vp;
 	struct vattr vattr;
-	off_t offset;
+	off_t offset, size;
 	int error, noneg;
 	int vfslocked;
 
@@ -1951,6 +1952,15 @@ lseek(td, uap)
 		VOP_UNLOCK(vp, 0);
 		if (error)
 			break;
+
+		/*
+		 * If the file references a disk device, then fetch
+		 * the media size and use that to determine the ending
+		 * offset.
+		 */
+		if (vattr.va_size == 0 && vp->v_type == VCHR &&
+		    fo_ioctl(fp, DIOCGMEDIASIZE, &size, cred, td) == 0)
+			vattr.va_size = size;
 		if (noneg &&
 		    (vattr.va_size > OFF_MAX ||
 		    (offset > 0 && vattr.va_size > OFF_MAX - offset))) {