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@xxxxxxxx> 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/
