On Thu, Apr 27, 2023 at 3:28 PM Amir Goldstein <amir73il@xxxxxxxxx> wrote: > > s_export_op > > On Thu, Apr 27, 2023 at 2:48 PM Jan Kara <jack@xxxxxxx> wrote: > > > > On Tue 25-04-23 16:01:05, Amir Goldstein wrote: > > > fanotify users do not always need to decode the file handles reported > > > with FAN_REPORT_FID. > > > > > > Relax the restriction that filesystem needs to support NFS export and > > > allow reporting file handles from filesystems that only support ecoding > > > unique file handles. > > > > > > For such filesystems, users will have to use the AT_HANDLE_FID of > > > name_to_handle_at(2) if they want to compare the object in path to the > > > object fid reported in an event. > > > > > > Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx> > > ... > > > diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c > > > index 8f430bfad487..a5af84cbb30d 100644 > > > --- a/fs/notify/fanotify/fanotify_user.c > > > +++ b/fs/notify/fanotify/fanotify_user.c > > > @@ -1586,11 +1586,9 @@ static int fanotify_test_fid(struct dentry *dentry) > > > * We need to make sure that the file system supports at least > > > * encoding a file handle so user can use name_to_handle_at() to > > > * compare fid returned with event to the file handle of watched > > > - * objects. However, name_to_handle_at() requires that the > > > - * filesystem also supports decoding file handles. > > > + * objects, but it does not need to support decoding file handles. > > > */ > > > - if (!dentry->d_sb->s_export_op || > > > - !dentry->d_sb->s_export_op->fh_to_dentry) > > > + if (!dentry->d_sb->s_export_op) > > > return -EOPNOTSUPP; > > > > So AFAICS the only thing you require is that s_export_op is set to > > *something* as exportfs_encode_inode_fh() can deal with NULL ->encode_fh > > just fine without any filesystem cooperation. What is the reasoning behind > > the dentry->d_sb->s_export_op check? Is there an implicit expectation that > > if s_export_op is set to something, the filesystem has sensible > > i_generation? Or is it just a caution that you don't want the functionality > > to be enabled for unexpected filesystems? > > A little bit of both. > Essentially, I do not want to use the generic encoding unless the filesystem > opted-in to say "This is how objects should be identified". > > The current fs that have s_export_op && !s_export_op->encode_fh > practically make that statement because they support NFS export > (i.e. they implement fh_to_dentry()). > > I don't like the implicit fallback to generic encoding, especially when > introducing this new functionality of encode_fid(). > > Before posting this patch set I had two earlier revisions. > One that changed the encode_fh() to mandatory and converted > all the INO32_GEN fs to explicitly set > s_export_op.encode_fh = generic_encode_ino32_fh, > And one that marked all the INO32_GEN fs with > s_export_op.flags = EXPORT_OP_ENCODE_INO32_GEN > in both cases there was no blind fallback to INO32_GEN. > > But in the end, these added noise without actual value so > I dropped them, because the d_sb->s_export_op check is anyway > a pretty strong indication for opt-in to export fids. > > CC exportfs maintainers in case they have an opinion one > way or the other. > BTW, the other reason I chose this requirement is circular - this is the same requirement for exporting fids to user with AT_HANDLE_FID and the two FAN_REPORT_FID should be aligned with users ability to get fid with name_to_handle_at(). Another reasonable requirement would have been: * !AT_HANDLE_FID requires ->fh_to_dentry (as current code) * AT_HANDLE_FID requires either ->fh_to_dentry or encode_fh Thanks, Amir.
