From: "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> To: NeilBrown <neilb@suse.com> Cc: mtk.manpages@gmail.com, linux-man@vger.kernel.org, "linux-nfs@vger.kernel.org" <linux-nfs@vger.kernel.org>, "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>, Lennart Poettering <lennart@poettering.net>, Peng Tao <tao.peng@primarydata.com> Subject: Re: [manpages PATCH] open_by_handle_at: clarifications needed due to NFS reexport Date: Wed, 22 Nov 2017 17:48:55 +0100 [thread overview] Message-ID: <52c5800b-150a-7ec9-133b-6c32e97249f4@gmail.com> (raw) In-Reply-To: <87wp2j1ggu.fsf@notabene.neil.brown.name> Hello Neil, On 11/21/2017 10:15 PM, NeilBrown wrote: > > The recent addition of NFS re-export and the possibility of > using name_to_handle_at() on an NFS filesystem raises issues > with name_to_handle_at() which have not been properly documented. > > Getting the filehandle for an untriggered automount point is > arguably meaningless and in certainly not supported by NFS. > name_to_handle_at() will return -EOVERFLOW even though the > requested "handle_bytes" is large enough. This is an unfortunate > overloading of the error code, but is manageable. > > So clarify this and also note that the mount_id is returned > when EOVERFLOW is reported. > > Thought: it would be nice if mount_id were returned in the > EOPNOTSUPP case too. I guess it is too late to fix that (?). > > Link: https://github.com/systemd/systemd/issues/7082 > Signed-off-by: NeilBrown <neilb@suse.com> Thanks! Patch applied. Cheers, Michael PS And meta-thanks for thinking to send me the steady small stream of man-pages patches that you do. > --- > man2/open_by_handle_at.2 | 25 +++++++++++++++++++++++++ > 1 file changed, 25 insertions(+) > > diff --git a/man2/open_by_handle_at.2 b/man2/open_by_handle_at.2 > index 91300e80fe24..9a30dd2ed476 100644 > --- a/man2/open_by_handle_at.2 > +++ b/man2/open_by_handle_at.2 > @@ -109,6 +109,12 @@ and > is set to indicate the required size; > the caller can then use this information to allocate a structure > of the correct size (see EXAMPLE below). > +Some care is needed here as > +.BR EOVERFLOW > +can also indicate that no filehandle is available for this particular > +name in a filesystem which does normally support filehandle lookup. > +This case can be detected when EOVERFLOW is returned without > +handle_bytes being increased. > .PP > Other than the use of the > .IR handle_bytes > @@ -193,6 +199,10 @@ Opening the pathname in the fifth field of that record yields a file > descriptor for the mount point; > that file descriptor can be used in a subsequent call to > .BR open_by_handle_at (). > +.I mount_id > +is returned both for a successful call and for a call that results > +in the error > +.BR EOVERFLOW . > .PP > By default, > .BR name_to_handle_at () > @@ -206,6 +216,21 @@ is specified in > .I pathname > is dereferenced if it is a symbolic link > (so that the call returns a handle for the file referred to by the link). > +.PP > +.BR name_to_handle_at ) > +does not trigger a mount when the final component of the path is an > +automount point. When a filesystem supports both filehandles and > +automount points, a > +.BR name_to_handle_at () > +call on an automount point will return with error > +.BR EOVERFLOW > +without having increased > +.IR handle_bytes . > +This can happen since Linux 4.13 with NFS when accessing a directory > +which is on a separate filesystem on the server. > +.\" commit 20fa19027286983ab2734b5910c4a687436e0c31 > +In this case the automount can be triggered by adding a "/" to the end > +of the path. > .SS open_by_handle_at() > The > .BR open_by_handle_at () > -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/
WARNING: multiple messages have this Message-ID (diff)
From: "Michael Kerrisk (man-pages)" <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> To: NeilBrown <neilb-IBi9RG/b67k@public.gmane.org> Cc: mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, linux-man-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, "linux-nfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" <linux-nfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, "linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" <linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Lennart Poettering <lennart-mdGvqq1h2p+GdvJs77BJ7Q@public.gmane.org>, Peng Tao <tao.peng-7I+n7zu2hftEKMMhf/gKZA@public.gmane.org> Subject: Re: [manpages PATCH] open_by_handle_at: clarifications needed due to NFS reexport Date: Wed, 22 Nov 2017 17:48:55 +0100 [thread overview] Message-ID: <52c5800b-150a-7ec9-133b-6c32e97249f4@gmail.com> (raw) In-Reply-To: <87wp2j1ggu.fsf-wvvUuzkyo1HefUI2i7LXDhCRmIWqnp/j@public.gmane.org> Hello Neil, On 11/21/2017 10:15 PM, NeilBrown wrote: > > The recent addition of NFS re-export and the possibility of > using name_to_handle_at() on an NFS filesystem raises issues > with name_to_handle_at() which have not been properly documented. > > Getting the filehandle for an untriggered automount point is > arguably meaningless and in certainly not supported by NFS. > name_to_handle_at() will return -EOVERFLOW even though the > requested "handle_bytes" is large enough. This is an unfortunate > overloading of the error code, but is manageable. > > So clarify this and also note that the mount_id is returned > when EOVERFLOW is reported. > > Thought: it would be nice if mount_id were returned in the > EOPNOTSUPP case too. I guess it is too late to fix that (?). > > Link: https://github.com/systemd/systemd/issues/7082 > Signed-off-by: NeilBrown <neilb-IBi9RG/b67k@public.gmane.org> Thanks! Patch applied. Cheers, Michael PS And meta-thanks for thinking to send me the steady small stream of man-pages patches that you do. > --- > man2/open_by_handle_at.2 | 25 +++++++++++++++++++++++++ > 1 file changed, 25 insertions(+) > > diff --git a/man2/open_by_handle_at.2 b/man2/open_by_handle_at.2 > index 91300e80fe24..9a30dd2ed476 100644 > --- a/man2/open_by_handle_at.2 > +++ b/man2/open_by_handle_at.2 > @@ -109,6 +109,12 @@ and > is set to indicate the required size; > the caller can then use this information to allocate a structure > of the correct size (see EXAMPLE below). > +Some care is needed here as > +.BR EOVERFLOW > +can also indicate that no filehandle is available for this particular > +name in a filesystem which does normally support filehandle lookup. > +This case can be detected when EOVERFLOW is returned without > +handle_bytes being increased. > .PP > Other than the use of the > .IR handle_bytes > @@ -193,6 +199,10 @@ Opening the pathname in the fifth field of that record yields a file > descriptor for the mount point; > that file descriptor can be used in a subsequent call to > .BR open_by_handle_at (). > +.I mount_id > +is returned both for a successful call and for a call that results > +in the error > +.BR EOVERFLOW . > .PP > By default, > .BR name_to_handle_at () > @@ -206,6 +216,21 @@ is specified in > .I pathname > is dereferenced if it is a symbolic link > (so that the call returns a handle for the file referred to by the link). > +.PP > +.BR name_to_handle_at ) > +does not trigger a mount when the final component of the path is an > +automount point. When a filesystem supports both filehandles and > +automount points, a > +.BR name_to_handle_at () > +call on an automount point will return with error > +.BR EOVERFLOW > +without having increased > +.IR handle_bytes . > +This can happen since Linux 4.13 with NFS when accessing a directory > +which is on a separate filesystem on the server. > +.\" commit 20fa19027286983ab2734b5910c4a687436e0c31 > +In this case the automount can be triggered by adding a "/" to the end > +of the path. > .SS open_by_handle_at() > The > .BR open_by_handle_at () > -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/ -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html
next prev parent reply other threads:[~2017-11-22 16:49 UTC|newest] Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top 2017-11-21 21:15 [manpages PATCH] open_by_handle_at: clarifications needed due to NFS reexport NeilBrown 2017-11-21 21:15 ` NeilBrown 2017-11-22 16:48 ` Michael Kerrisk (man-pages) [this message] 2017-11-22 16:48 ` Michael Kerrisk (man-pages) 2017-11-23 23:53 ` [manpages PATCH] open_by_handle_at.2: clarify MAX_HANDLE_SZ NeilBrown 2017-11-23 23:53 ` NeilBrown 2017-11-24 8:34 ` Michael Kerrisk (man-pages) 2017-11-24 8:34 ` Michael Kerrisk (man-pages)
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