From: Amir Goldstein <amir73il@gmail.com>
To: Jan Kara <jack@suse.cz>
Cc: linux-fsdevel <linux-fsdevel@vger.kernel.org>
Subject: Re: [PATCH v2 11/16] fanotify: prepare to encode both parent and child fid's
Date: Wed, 26 Feb 2020 19:50:30 +0200 [thread overview]
Message-ID: <CAOQ4uxgW9Jcj_hG639nw=j0rFQ1fGxBHJJz=nHKTPBat=L+mXg@mail.gmail.com> (raw)
In-Reply-To: <20200226170705.GU10728@quack2.suse.cz>
On Wed, Feb 26, 2020 at 7:07 PM Jan Kara <jack@suse.cz> wrote:
>
> On Wed 26-02-20 13:53:06, Amir Goldstein wrote:
> > On Wed, Feb 26, 2020 at 12:23 PM Jan Kara <jack@suse.cz> wrote:
> > >
> > > > + __kernel_fsid_t fsid;
> > > > union {
> > > > /*
> > > > * We hold ref to this path so it may be dereferenced at any
> > >
> > > Here I disagree. IMO 'fsid' should be still part of the union below because
> > > the "object identification" is either struct path or (fsid + fh). I
> > > understand that you want to reuse fsid for the other file handle. But then
> > > I believe it should rather be done like:
> > >
> > > struct fanotify_fh {
> > > union {
> > > unsigned char fh[FANOTIFY_INLINE_FH_LEN];
> > > unsigned char *ext_fh;
> > > };
> > > };
> > >
> >
> > This I will do.
> >
> > > struct fanotify_fid {
> > > __kernel_fsid_t fsid;
> > > struct fanotify_fh object;
> > > struct fanotify_fh dir;
> > > }
> > >
> >
> > object and dir do not end up in the same struct.
>
> Right, ok.
>
> > object is in fanotify_event
> > dir is in the extended fanotify_name_event, but I can do:
> >
> > struct fanotify_fid {
> > __kernel_fsid_t fsid;
> > struct fanotify_fh fh;
> > }
> >
> > struct fanotify_event {
> > struct fsnotify_event fse;
> > u32 mask;
> > struct fanotify_fid_hdr fh;
> > struct fanotify_fid_hdr dfh;
> > union {
> > struct path path;
> > struct fanotify_fid object;
> > };
> > struct pid *pid;
> > };
> >
> > struct fanotify_name_event {
> > struct fanotify_event fae;
> > struct fanotify_fh dir;
> > struct qstr name;
> > unsigned char inline_name[FANOTIFY_INLINE_NAME_LEN];
> > };
>
> Looking at this I'm not quite happy either :-| E.g. 'dfh' contents here
> somewhat magically tells that this is not fanotify_event but
> fanotify_name_event. Also I agree that fsid hidden in 'object' is not ideal
> although I still dislike having it directly in fanotify_event as for path
> events it will not be filled and that can lead to confusion.
>
> I understand this is so convoluted because there are several constraints:
> 1) We don't want to grow event size unnecessarily.
> 2) We prefer allocating from dedicated slab cache
> 3) We have events of several types needing to store different kind of
> information.
>
> But seeing how things evolve I think we should consider relaxing some of
> the constraints to make the code easier to follow. How about having
> something like:
>
> struct fanotify_event {
> struct fsnotify_event fse;
> u32 mask;
> enum fanotify_event_type type;
> struct pid *pid;
> };
>
> where type would identify what kind of event we have. Then we would have
>
> struct fanotify_path_event {
> struct fanotify_event fae;
> struct path path;
> };
>
> struct fanotify_perm_path_event {
> struct fanotify_event fae;
> struct path path;
Any reason not to "inherit" from fanotify_path_event?
There is code that is generic to permission and non-permission path
events that accesses event->path and I wouldn't
want to make that code two cases instead of just one.
> unsigned short response;
> unsigned short state;
> int fd;
> };
>
> struct fanotify_fh {
> u8 type;
> u8 len;
That's a 6 bytes hole! and then there are two of those
in object_fh and dir_fh.
That is why I stored the header in separate from the fh itself
so that two headers could pack up nicely and yes,
I also used the headers as an event type indication.
> union {
> unsigned char fh[FANOTIFY_INLINE_FH_LEN];
> unsigned char *ext_fh;
> };
> };
>
> struct fanotify_fid_event {
> struct fanotify_event fae;
> __kernel_fsid_t fsid;
> struct fanotify_fh object_fh;
> };
>
> struct fanofify_name_event {
> struct fanotify_event fae;
> __kernel_fsid_t fsid;
> struct fanotify_fh object_fh;
Again, any reason not to "inherit" from fanotify_fid_event?
There is plenty of code that is common to fid and name events
because name events are also fid events.
> struct fanotify_fh dir_fh;
> u8 name_len;
> char name[0];
> };
>
> WRT size, this would grow fanotify_fid_event by 1 long on 64-bits,
> fanotify_path_event would be actually smaller by 1 long, fanofify_name_event
> would be smaller but that's not really comparable because you chose a
> solution with fixed-inline length while I'd just go with allocating from
> kmalloc when we have to store the name.
OK. Same an inotify.
I guess I started with the name_snapshot thing that was really fixed-size
event and then reused the same construct without the snapshot, but I
guess we can do away with the inline name.
>
> In terms of kmalloc caches, we would need three: for path, perm_path, fid
> events, I'd allocate name events from generic kmalloc caches.
>
> So overall I think this would be better. The question is whether the
> resulting code will really be more readable. I hope so because the
> structures are definitely nicer this way and things belonging logically
> together are now together. But you never know until you convert the code...
> Would you be willing to try this refactoring?
Yes, but I would like to know what you think about the two 6 byte holes
Just let that space be wasted for the sake of nicer abstraction?
It seems like too much to me.
Thanks,
Amir.
next prev parent reply other threads:[~2020-02-26 17:50 UTC|newest]
Thread overview: 65+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-17 13:14 [PATCH v2 00/16] Fanotify event with name info Amir Goldstein
2020-02-17 13:14 ` [PATCH v2 01/16] fsnotify: tidy up FS_ and FAN_ constants Amir Goldstein
2020-02-17 13:14 ` [PATCH v2 02/16] fsnotify: factor helpers fsnotify_dentry() and fsnotify_file() Amir Goldstein
2020-02-25 13:46 ` Jan Kara
2020-02-25 14:27 ` Amir Goldstein
2020-02-26 13:59 ` Jan Kara
2020-02-17 13:14 ` [PATCH v2 03/16] fsnotify: funnel all dirent events through fsnotify_name() Amir Goldstein
2020-02-17 13:14 ` [PATCH v2 04/16] fsnotify: use helpers to access data by data_type Amir Goldstein
2020-02-17 13:14 ` [PATCH v2 05/16] fsnotify: simplify arguments passing to fsnotify_parent() Amir Goldstein
2020-02-19 10:50 ` kbuild test robot
2020-02-19 11:11 ` Amir Goldstein
2020-02-17 13:14 ` [PATCH v2 06/16] fsnotify: pass dentry instead of inode for events possible on child Amir Goldstein
2020-02-17 13:14 ` [PATCH v2 07/16] fsnotify: replace inode pointer with tag Amir Goldstein
2020-02-26 8:20 ` Jan Kara
2020-02-26 9:34 ` Amir Goldstein
2020-02-26 8:52 ` Jan Kara
2020-02-17 13:14 ` [PATCH v2 08/16] fanotify: merge duplicate events on parent and child Amir Goldstein
2020-02-26 9:18 ` Jan Kara
2020-02-26 12:14 ` Amir Goldstein
2020-02-26 14:38 ` Jan Kara
2021-01-22 13:59 ` fanotify_merge improvements Amir Goldstein
2021-01-23 13:30 ` Amir Goldstein
2021-01-25 13:01 ` Jan Kara
2021-01-26 16:21 ` Amir Goldstein
2021-01-27 11:24 ` Jan Kara
2021-01-27 12:57 ` Amir Goldstein
2021-01-27 15:15 ` Jan Kara
2021-01-27 18:03 ` Amir Goldstein
2021-01-28 10:27 ` Jan Kara
2021-01-28 18:50 ` Amir Goldstein
2020-02-17 13:14 ` [PATCH v2 09/16] fanotify: fix merging marks masks with FAN_ONDIR Amir Goldstein
2020-02-17 13:14 ` [PATCH v2 10/16] fanotify: send FAN_DIR_MODIFY event flavor with dir inode and name Amir Goldstein
2020-02-17 13:14 ` [PATCH v2 11/16] fanotify: prepare to encode both parent and child fid's Amir Goldstein
2020-02-26 10:23 ` Jan Kara
2020-02-26 11:53 ` Amir Goldstein
2020-02-26 17:07 ` Jan Kara
2020-02-26 17:50 ` Amir Goldstein [this message]
2020-02-27 9:06 ` Amir Goldstein
2020-02-27 11:27 ` Jan Kara
2020-02-27 12:12 ` Amir Goldstein
2020-02-27 13:30 ` Jan Kara
2020-02-27 14:06 ` Amir Goldstein
2020-03-01 16:26 ` Amir Goldstein
2020-03-05 15:49 ` Jan Kara
2020-03-06 11:19 ` Amir Goldstein
2020-03-08 7:29 ` Amir Goldstein
2020-03-18 17:51 ` Jan Kara
2020-03-18 18:50 ` Amir Goldstein
2020-03-19 9:30 ` Jan Kara
2020-03-19 10:07 ` Amir Goldstein
2020-03-30 19:29 ` Amir Goldstein
2020-02-27 11:01 ` Jan Kara
2020-02-17 13:14 ` [PATCH v2 12/16] fanotify: record name info for FAN_DIR_MODIFY event Amir Goldstein
2020-02-17 13:14 ` [PATCH v2 13/16] fanotify: report " Amir Goldstein
2020-02-19 9:43 ` kbuild test robot
2020-02-19 10:17 ` kbuild test robot
2020-02-19 11:22 ` Amir Goldstein
2020-04-16 12:16 ` Michael Kerrisk (man-pages)
2020-04-20 15:53 ` Jan Kara
2020-04-20 18:45 ` Amir Goldstein
2020-04-20 18:47 ` Michael Kerrisk (man-pages)
2020-02-17 13:14 ` [PATCH v2 14/16] fanotify: report parent fid + name with FAN_REPORT_NAME Amir Goldstein
2020-02-17 13:14 ` [PATCH v2 15/16] fanotify: refine rules for when name is reported Amir Goldstein
2020-02-17 13:14 ` [BONUS][PATCH v2 16/16] fanotify: support limited functionality for unprivileged users Amir Goldstein
2020-02-20 22:10 ` [PATCH v2 00/16] Fanotify event with name info Matthew Bobrowski
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