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Re: [PATCH 3/3] xfs_io: implement inode '-n' and [num] argument

To: Brian Foster <bfoster@xxxxxxxxxx>
Subject: Re: [PATCH 3/3] xfs_io: implement inode '-n' and [num] argument
From: Carlos Maiolino <cmaiolino@xxxxxxxxxx>
Date: Fri, 9 Oct 2015 15:25:26 +0200
Cc: xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20151009123613.GA27982@xxxxxxxxxxxxxxx>
Mail-followup-to: Brian Foster <bfoster@xxxxxxxxxx>, xfs@xxxxxxxxxxx
References: <1443186467-20110-1-git-send-email-cmaiolino@xxxxxxxxxx> <1443186467-20110-4-git-send-email-cmaiolino@xxxxxxxxxx> <20151006170055.GD63205@xxxxxxxxxxxxxxx> <20151009083313.GA28373@xxxxxxxxxx> <20151009123613.GA27982@xxxxxxxxxxxxxxx>
User-agent: Mutt/1.5.23 (2014-03-12)
Hey

> > 
> > Hmm, I don't think so, I need getopt() to setup optind for this.
> > 
> 
> I don't see how that matters. That code can stay in the first patch. I'm
> just saying patch 1 should probably implement the core/default
> functionality, and obviously whatever supporting code is necessary to
> make that happen. For example, that could mean that the above
> ret_isvalid = 1 block goes away, the code executes in this mode by
> default, and the subsequent patches implement alternate branches as
> necessary to alter behavior.
> 

Right, I think I misunderstood your previous comment, when you said about this
going first, I thought about code ordering, not patch ordering. In this point I
agree with you.

> In other words, the (pseudo)code can start off looking like this:
> 
>       userino = ...;
> 
>       ...
> 
>       bulkreq = ...
>       xfsctl(..., XFS_IOC_FSBULKSTAT_SINGLE, ...);
>       printf("Valid inode: ...");
>       return 0;
> 
> ... then patch 2 comes along an adds a next option:
> 
>       int cmd = XFS_IOC_FSBULKSTAT_SINGLE;
> 
>       while (getopt() = ...) {
>               if (next)
>                       cmd = XFS_IOC_FSBULKSTAT;
>       }
>       userino = ...;
> 
>       ...
> 
>       bulkreq = ...
>       xfsctl(..., cmd, ...);
>       printf("%s inode: ...", next ? "Next" : "Valid", ...);
>       return 0;
> 
> ... and so on. Patch 3 comes along and adds more command line options
> and an alternate FSNUMBERS branch before the bulkstat xfsctl(). That
> branch ends with a return 0, so there's no need to put the core
> mechanism bits above into an 'if (ret_isvalid).'
> 
Makes sense

> The alternative is to just squash everything to one patch, which is
> probably reasonable too. I still think the end result can be simplified
> and reduced to something like the above though.
> 
> > > > +
> > > > +       if (userino)
> > > > +               if (*p != '\0') {
> > > > +                       printf("[num] must be a valid number\n");
> > > > +                       exitcode = 1;
> > > > +                       return 0;
> > > > +               }
> > > > +
> > > >         if (ret_lsize || ret_largest) {
> > > > +
> > > > +               bulkreq.lastip = &last;
> > > > +               bulkreq.icount = 1024; /* User-defined maybe!? */
> > > > +               bulkreq.ubuffer = &igroup;
> > > > +               bulkreq.ocount = &count;
> > > > +
> > > >                 for (;;) {
> > > >                         if (xfsctl(file->name, file->fd, 
> > > > XFS_IOC_FSINUMBERS,
> > > >                                         &bulkreq)) {
> > > > @@ -806,7 +831,7 @@ inode_f(
> > > >                                 exitcode = 1;
> > > >                                 return 0;
> > > >                         }
> > > > -                       if (count < XFS_INODES_PER_CHUNK && count > 0)
> > > > +                       if (count < 1024 && count > 0)
> > > >                                 lastgrp = count;
> > > 
> > > Ok, that sort of addresses my question on patch 1. I guess this is a
> > > record count rather than an inode count as well. In that case, what
> > > happens if the fs has an exact multiple of 1024 inode records?
> > > 
> > Yes, it's a record count, each record contains a single inode chunk.
> > regarding the exactly multiple of 1024 chunks, AFAIK it will fit all the 
> > 1024
> > records in a single array, which is exactly the size of the array I'm using
> > here, and, next call to xfsctl, will return a 0 records count, making the 
> > look
> > to exit.
> > 
> 
> Ok, that's what I would expect up to that point. To be more clear, when
> is lastgrp ever set? Further, what happens if xfsctl() somewhere down
> the road decides to memset(..., 0, ...) bulkreq.ubuffer (for example)
> when count is set to 0?
> 
> For example, here's a quick experiment on an fs with precisely 1024
> inode records:
> 
> # ./io/xfs_io -c "inode -l" /mnt/
> Largest inode: 1070
> # find /mnt/ -inum 1070 -print
> #
> 
> Oops! :) After adding a few more records:
> 
> # ./io/xfs_io -c "inode -l" /mnt/
> Largest inode: 971014
> # find /mnt/ -inum 971014 -print
> /mnt/tmp/128
> #
> 
> > > BTW, I think this should probably be set correctly when it is introduced
> > > rather than set to a value and changed in a subsequent patch.
> > 
> > Yes, I just forgot to change this in the first patch, see my comment in 
> > patch 1.
> > 
> > > 
> > > >                         if (!count)
> > > >                                 break;
> > > > @@ -822,8 +847,47 @@ inode_f(
> > > >                 else
> > > >                         printf(_("Largest inode: %llu\n"), lastino);
> > > >  
> > > > +               return 0;
> > > > +       }
> > > > +
> > > > +       /* Setup bulkreq for -n or [num] only */
> > > > +       last = userino;
> > > > +       bulkreq.lastip = &last;
> > > > +       bulkreq.icount = 1;
> > > > +       bulkreq.ubuffer = &bstat;
> > > > +       bulkreq.ocount = &count;
> > > > +
> > > > +       if (ret_next) {
> > > > +               if (xfsctl(file->name, file->fd, XFS_IOC_FSBULKSTAT, 
> > > > &bulkreq)) {
> > > > +                       if (errno == EINVAL)
> > > > +                               printf("Invalid or non-existent 
> > > > inode\n");
> > > > +                       else
> > > > +                               perror("XFS_IOC_FSBULKSTAT");
> > > > +                       exitcode = 1;
> > > > +                       return 0;
> > > > +               }
> > > > +
> > > > +               if (!bstat.bs_ino) {
> > > > +                       printf("There are no further inodes in the 
> > > > filesystem\n");
> > > > +                       return 0;
> > > > +               }
> > > 
> > > The above should technically check the output count rather than the
> > > inode number, right?
> > > 
> > If I use the inode count, I can get an 'allocated but free' inode, which is 
> > not
> > the intention here.
> >  
> 
> I don't think bulkstat returns unused (but allocated) inodes. Most of
> the inode information would be invalid/undefined. Indeed, from
> xfs_bulkstat_ag_ichunk():
> 
>                 /* Skip if this inode is free */
>                 if (XFS_INOBT_MASK(chunkidx) & irbp->ir_free)
>                         continue;
> 
> Brian
> 

I'll check the another points on Monday, thanks for the review Brian.

have a good weekend

-- 
Carlos

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