Add zfs_open()/zfs_close()

In the original implementation the zfs_open()/zfs_close() hooks
were dropped for simplicity.  This was functional but not 100%
correct with the expected ZFS sematics.  Updating and re-adding the
zfs_open()/zfs_close() hooks resolves the following issues.

1) The ZFS_APPENDONLY file attribute is once again honored.  While
there are still no Linux tools to set/clear these attributes once
there are it should behave correctly.

2) Minimal virus scan file attribute hooks were added.  Once again
this support in disabled but the infrastructure is back in place.

3) Most importantly correctly handle assigning files which were
opened syncronously to the intent log.  Without this change O_SYNC
modifications could be lost during a system crash even though they
were marked synchronous.

include/sys/zfs_vnops.h

@@ -36,6 +36,8 @@
 extern "C" {
 #endif
 
+extern int zfs_open(struct inode *ip, int mode, int flag, cred_t *cr);
+extern int zfs_close(struct inode *ip, int flag, cred_t *cr);
 extern int zfs_read(struct inode *ip, uio_t *uio, int ioflag, cred_t *cr);
 extern int zfs_write(struct inode *ip, uio_t *uio, int ioflag, cred_t *cr);
 extern int zfs_access(struct inode *ip, int mode, int flag, cred_t *cr);

module/zfs/zfs_vnops.c

@@ -163,6 +163,76 @@
  *	return (error);			// done, report error
  */
 
+/*
+ * Virus scanning is unsupported.  It would be possible to add a hook
+ * here to performance the required virus scan.  This could be done
+ * entirely in the kernel or potentially as an update to invoke a
+ * scanning utility.
+ */
+static int
+zfs_vscan(struct inode *ip, cred_t *cr, int async)
+{
+	return (0);
+}
+
+/* ARGSUSED */
+int
+zfs_open(struct inode *ip, int mode, int flag, cred_t *cr)
+{
+	znode_t	*zp = ITOZ(ip);
+	zfs_sb_t *zsb = ITOZSB(ip);
+
+	ZFS_ENTER(zsb);
+	ZFS_VERIFY_ZP(zp);
+
+	/* Honor ZFS_APPENDONLY file attribute */
+	if ((mode & FMODE_WRITE) && (zp->z_pflags & ZFS_APPENDONLY) &&
+	    ((flag & O_APPEND) == 0)) {
+		ZFS_EXIT(zsb);
+		return (EPERM);
+	}
+
+	/* Virus scan eligible files on open */
+	if (!zfs_has_ctldir(zp) && zsb->z_vscan && S_ISREG(ip->i_mode) &&
+	    !(zp->z_pflags & ZFS_AV_QUARANTINED) && zp->z_size > 0) {
+		if (zfs_vscan(ip, cr, 0) != 0) {
+			ZFS_EXIT(zsb);
+			return (EACCES);
+		}
+	}
+
+	/* Keep a count of the synchronous opens in the znode */
+	if (flag & O_SYNC)
+		atomic_inc_32(&zp->z_sync_cnt);
+
+	ZFS_EXIT(zsb);
+	return (0);
+}
+EXPORT_SYMBOL(zfs_open);
+
+/* ARGSUSED */
+int
+zfs_close(struct inode *ip, int flag, cred_t *cr)
+{
+	znode_t	*zp = ITOZ(ip);
+	zfs_sb_t *zsb = ITOZSB(ip);
+
+	ZFS_ENTER(zsb);
+	ZFS_VERIFY_ZP(zp);
+
+	/* Decrement the synchronous opens in the znode */
+	if (flag & O_SYNC)
+		zp->z_sync_cnt = 0;
+
+	if (!zfs_has_ctldir(zp) && zsb->z_vscan && S_ISREG(ip->i_mode) &&
+	    !(zp->z_pflags & ZFS_AV_QUARANTINED) && zp->z_size > 0)
+		VERIFY(zfs_vscan(ip, cr, 1) == 0);
+
+	ZFS_EXIT(zsb);
+	return (0);
+}
+EXPORT_SYMBOL(zfs_close);
+
 #if defined(_KERNEL)
 /*
  * When a file is memory mapped, we must keep the IO data synchronized

module/zfs/zpl_file.c

@@ -29,6 +29,37 @@
 #include <sys/zpl.h>
 
 
+static int
+zpl_open(struct inode *ip, struct file *filp)
+{
+	cred_t *cr;
+	int error;
+
+	cr = (cred_t *)get_current_cred();
+	error = -zfs_open(ip, filp->f_mode, filp->f_flags, cr);
+	put_cred(cr);
+	ASSERT3S(error, <=, 0);
+
+	if (error)
+		return (error);
+
+	return generic_file_open(ip, filp);
+}
+
+static int
+zpl_release(struct inode *ip, struct file *filp)
+{
+	cred_t *cr;
+	int error;
+
+	cr = (cred_t *)get_current_cred();
+	error = -zfs_close(ip, filp->f_flags, cr);
+	put_cred(cr);
+	ASSERT3S(error, <=, 0);
+
+	return (error);
+}
+
 static int
 zpl_readdir(struct file *filp, void *dirent, filldir_t filldir)
 {
@@ -316,7 +347,8 @@ const struct address_space_operations zpl_address_space_operations = {
 };
 
 const struct file_operations zpl_file_operations = {
-	.open		= generic_file_open,
+	.open		= zpl_open,
+	.release	= zpl_release,
 	.llseek		= generic_file_llseek,
 	.read		= zpl_read,
 	.write		= zpl_write,