Add d_off support for multiple filesystems.

The d_off field has been added to the dirent structure recently.
Currently filesystems don't support this feature.  Support has been
added and tested for zfs, ufs, ext2fs, fdescfs, msdosfs and unionfs.
A stub implementation is available for cd9660, nandfs, udf and
pseudofs but hasn't been tested.

Motivation for this feature: our usecase is for a userspace nfs server
(nfs-ganesha) with zfs.  At the moment we cache direntry offsets by
calling lseek once per entry, with this patch we can get the offset
directly from getdirentries(2) calls which provides a significant
speedup.

Submitted by:	Jack Halford <jack@gandi.net>
Reviewed by:	mckusick, pfg, rmacklem (previous versions)
Sponsored by:	Gandi.net
MFC after:	1 week
Differential revision:	https://reviews.freebsd.org/D17917

1 files changed, 3 insertions, 0 deletions

diff --git a/sys/fs/udf/udf_vnops.c b/sys/fs/udf/udf_vnops.c
index 6e7706c5c7c5..30558cf86931 100644
--- a/sys/fs/udf/udf_vnops.c
+++ b/sys/fs/udf/udf_vnops.c
@@ -846,6 +846,7 @@ udf_readdir(struct vop_readdir_args *a)
 			dir.d_name[1] = '\0';
 			dir.d_namlen = 1;
 			dir.d_reclen = GENERIC_DIRSIZ(&dir);
+			dir.d_off = 1;
 			uiodir.dirent = &dir;
 			error = udf_uiodir(&uiodir, dir.d_reclen, uio, 1);
 			if (error)
@@ -858,6 +859,7 @@ udf_readdir(struct vop_readdir_args *a)
 			dir.d_name[2] = '\0';
 			dir.d_namlen = 2;
 			dir.d_reclen = GENERIC_DIRSIZ(&dir);
+			dir.d_off = 2;
 			uiodir.dirent = &dir;
 			error = udf_uiodir(&uiodir, dir.d_reclen, uio, 2);
 		} else {
@@ -867,6 +869,7 @@ udf_readdir(struct vop_readdir_args *a)
 			dir.d_type = (fid->file_char & UDF_FILE_CHAR_DIR) ?
 			    DT_DIR : DT_UNKNOWN;
 			dir.d_reclen = GENERIC_DIRSIZ(&dir);
+			dir.d_off = ds->this_off;
 			uiodir.dirent = &dir;
 			error = udf_uiodir(&uiodir, dir.d_reclen, uio,
 			    ds->this_off);