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Message-ID: <20170629185022.GB4178@fieldses.org> Date: Thu, 29 Jun 2017 14:50:22 -0400 From: "J. Bruce Fields" <bfields@...ldses.org> To: "Darrick J. Wong" <darrick.wong@...cle.com> Cc: William Koh <kkc6196@...com>, Andreas Dilger <adilger@...ger.ca>, Theodore Ts'o <tytso@....edu>, linux-ext4 <linux-ext4@...r.kernel.org>, lkml <linux-kernel@...r.kernel.org>, Kernel Team <Kernel-team@...com>, linux-fsdevel <linux-fsdevel@...r.kernel.org>, Trond Myklebust <trond.myklebust@...marydata.com>, xfs <linux-xfs@...r.kernel.org> Subject: Re: [PATCH] fs: ext4: inode->i_generation not assigned 0. On Thu, Jun 29, 2017 at 02:30:53PM -0400, J. Bruce Fields wrote: > On Thu, Jun 29, 2017 at 10:25:28AM -0700, Darrick J. Wong wrote: > > Was there ever a version of NFS (or more generally callers of the > > exportfs code) that couldn't deal with i_generation in the file handle, > > and therefore we invented this generation hack to work around the loss > > of the generation information? > > > > There's a comment in xfs_fs_encode_fh about not supporting 64bit inodes > > with subtree_check (which seems to require one ino/gen pair for the file > > and a second pair for the file's parent) on NFSv2 because v2 doesn't > > provide enough space for all the file handle information, but that's the > > furthest I got with lazy-mining the git history. :) > > There's a comment in fs/ext4/super.c:ext4_nfs_get_inode > > * Currently we don't know the generation for parent directory, so > * a generation of 0 means "accept any" > > But I don't see that used. > > It was used once upon a time; I see it actually used in old 2.5 code in > nfsd_get_dentry. Hm. Oh, maybe it's here in fs/libfs.c:generic_fh_to_parent: switch (fh_type) { case FILEID_INO32_GEN_PARENT: inode = get_inode(sb, fid->i32.parent_ino, (fh_len > 3 ? fid->i32.parent_gen : 0)); break; } I'm not sure under what conditions that filehandle encoding is used. --b.
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