PR/60135 CVS commit: src/external/cddl/osnet/dist/uts/common/fs/zfs

["YAMAMOTO Takashi" <yamt%netbsd.org@localhost>]

The following reply was made to PR kern/60135; it has been noted by GNATS.

From: "YAMAMOTO Takashi" <yamt%netbsd.org@localhost>
To: gnats-bugs%gnats.NetBSD.org@localhost
Cc: 
Subject: PR/60135 CVS commit: src/external/cddl/osnet/dist/uts/common/fs/zfs
Date: Fri, 27 Mar 2026 13:50:52 +0000

 Module Name:	src
 Committed By:	yamt
 Date:		Fri Mar 27 13:50:52 UTC 2026
 
 Modified Files:
 	src/external/cddl/osnet/dist/uts/common/fs/zfs: zfs_vfsops.c
 	    zfs_vnops.c
 
 Log Message:
 zfs: use 32-bit st_dev for stat(2)
 
 while dev_t is 64-bit on NetBSD since the merge of
 christos-time_t branch in 2009, we only use the lower
 32-bit of it, at least for the purpose of specifying
 a device in the kernel.
 
 however, dev_t is also used as a file system id. eg. st_dev
 reported by stat(2). as zfs has no device to naturally represent
 its file system, currently it reports 56-bit guid of the file
 system for the purpose.
 
 unfortunately, some user applications still consider it as
 a good old device id and assumes operations like
 makedev(major(dev),minor(dev)) preserves the value.
 it doesn't hold for NetBSD's implementation of makedev and
 friends, which only honors the lower 32-bit of the dev_t.
 
 this commit makes zfs report fsid with the high 32-bit zeros
 to avoid the issues in such applications. namely, this fixes an
 issue with rsync, reported by HIROSE yuuji on a japanese ML [1]
 in 2024. you can find his reproduce recipe below. i was able to
 reproduce the issue with rsync-3.4.1 from pkgsrc.
 
 maybe we can "fix" our, at least userland-visible version of,
 makedev and friends to provide full 64-bit round-trip as some
 of other platforms do. (eg. glibc, freebsd)
 although it might be an improvement and can benefit other things
 like nfs v3, it isn't an alternative to this fix because it
 doesn't fix existing application binaries built with the current
 version of the macros.
 
 note: this commit also changes statvfs f_fsid. as f_fsid is a long,
 before this change, we were truncating the value only on 32-bit ports.
 
 note: this commit doesn't change the "netbsd-extended" fsid
 (f_fsidx), which is used for nfs file handles.
 
 note: this commit would cause a flag day for applications which
 somehow save st_dev of files. are there such applications?
 
 note: this commit would increase the chance of fsid conflicts.
 currently zfs ensures its fsids unique within zfs, but not with
 other netbsd file systems. with this commit, there can be conflict
 even within zfs. (mentioned in PR/60135)
 
 ```
 rm -rf src
 rm -rf dest
 mkdir -p src/a/b/c
 mkdir -p src/1/2/3
 mkdir dest
 rsync -avx --delete src dest
 rm -r src/1
 rsync -avx --delete src dest
 test -d dest/src/1 && echo "this directory should have been removed"
 ```
 
 [1] http://www.re.soum.co.jp/~jun/welcome.html#netbsd
 
 related to PR/60135
 https://gnats.netbsd.org/60135
 
 
 To generate a diff of this commit:
 cvs rdiff -u -r1.34 -r1.35 \
     src/external/cddl/osnet/dist/uts/common/fs/zfs/zfs_vfsops.c
 cvs rdiff -u -r1.97 -r1.98 \
     src/external/cddl/osnet/dist/uts/common/fs/zfs/zfs_vnops.c
 
 Please note that diffs are not public domain; they are subject to the
 copyright notices on the relevant files.