[Rpm-maint] FSM hooks for rpm plugin

Panu Matilainen pmatilai at laiskiainen.org
Thu Mar 7 17:41:58 UTC 2013


On 03/07/2013 03:59 PM, Reshetova, Elena wrote:
> On 03/06/2013 05:01 PM, Reshetova, Elena wrote:
>>> What's missing is that another call to the hook is needed in
>>> fsmMkdirs() for the unowned directories, and there we should perhaps pass
>>> in the "unowned"
>>> aspect somehow. Having a separate argument for that seems like an
>>> overkill though... maybe we could pass that piece of info in the
>>> action argument instead. One possibility could be adding a new
>>> action, eg FA_CREATEUNOWNED that could be used for unowned
>>> directories (and files, but there aren't any currently). Or we could
>>> define the action as a partial bitfield: leave the existing actions
>>> alone but reserve the "upper" byte for special bits, such as
>>> "unknown". I had some other use-case for turning it into (partial) bitfield
>>> but can't remember what it was right now.
>>
>> I think bitfield would be better in this case: if one start introduce
>> actions FA_CREATEUNOWNED, then why not have FA_CREATELINK and etc. I
>> will add hook calling for mkdirs, but I think it is better that you do
>> a change of actions in a separate commit.
>
>> Sure, and I agree bitfield seems like the better option as it'll allow
>> cramming a whole lot more information in there. There's a whole lot of
>> redundancy in the current actions (all the skip cases for example) and some
>> of the values are totally unused as well.
>
>> As the file actions aren't really exported in the API in a way that somebody
>> could actually be using them, we might be able to get away with just
>> redefining the whole thing as a bitfield and add the old symbols as defines
>> or'ed together from the bits. But I'll need to think about it some more, in
>> any case such >a total conversion is not required in order to add a handful
>> of bits right now.
>
> Ok, I think if you can add an "unowned" bit to it for a start, this can be a
> good beginning and then even the existing pre/post hooks can get one less
> argument, which is great.

Sure, will do.

>
>> Continue on bit field idea, it would be great for plugins to get the
>> basic info about  the file acted upon from action also: so , if we are
>> adding unowned bit, should the basic bits indicating hard or sym link
>> be also supplied in action? Like action could point that it is
>> creation of symlink or removal of hard link. Is it too bad idea?
>
>> Hmm, but we already pass the mode (and planning to pass the whole stat
>> struct) around, so you can tell whether its a symlink, directory or something
>> else. Hardlinks are the more special case but you can tell them apart from
>> others by st_nlinks from the stat struct. Except that you dont necessarily
>> know which one is "real" file without extra tracking... unless st_nlinks is 1
>> for real >files (including the first
>> hardlink) and more for the actual links. I'm not sure if that's the case even
>> already, but should be possible to arrange at least.
>
> I am quite sure you can't tell it from stat struct which is real file and
> which is hard link: the value for st_nlinks is stored in inode and not in
> dentry in my understanding, that's why it isn't really easy for plugin to
> detect the hard links, so indicator would be a plus...

A file is a hard-link if (S_ISREG(st->st_mode) && st->st_nlink > 1) is 
true. When erasing, we get this info from filesystem so that remains 
accurate (the last one would be seen as the "real" file). On 
installation the stat struct of a file is made up by rpm, so we can pass 
whatever we want in there. Currently st_nlink for hardlinks equals the 
total number of links a file will have, but we can easily change that to 
the number of *current* links so that it better matches reality. Ie the 
first one will have st_nlink == 1 so it will be seen as the real file, 
the rest will st_nlink++ each. See attached patch for a quick 
implementation of this.

	- Panu -





-------------- next part --------------
A non-text attachment was scrubbed...
Name: fsm-nlinks-0.patch
Type: text/x-patch
Size: 2226 bytes
Desc: not available
URL: <http://lists.rpm.org/pipermail/rpm-maint/attachments/20130307/d06506f4/attachment.bin>


More information about the Rpm-maint mailing list