On 2014-07-10, Gary Johnson wrote:
> On 2014-07-10, Gary Johnson wrote:
> > On 2014-07-10, Bram Moolenaar wrote:
>
> > > Did you check the inode numbers on the files? ls --inode.
> > > Vim checks if files are the same, ignoring links, by comparing the inode
> > > and devide number.
> >
> > I was going to try that before, but thought it unnecessary since the
> > sizes and modification times were different. I tried it just now,
> > changing nightly.0 to nightly.1 because the backups have rotated.
> >
> > $ ls -il .snapshot/nightly.1/.configfiles/profile.common .configfiles/profile.common
> > 14988947 -rwx------ 1 gary gary 2269 Jul 9 15:00 .configfiles/profile.common
> > 14988947 -rwx------ 1 gary gary 2992 Jul 7 10:07 .snapshot/nightly.1/.configfiles/profile.common
> >
> > Sure enough, the inode numbers are the same! I then tried to find
> > out something about the file systems to which those directories
> > belong, but I don't understand the results.
> >
> > $ df -h .configfiles
> > Filesystem Size Used Avail Use% Mounted on
> > fserver1b:/vol/users/gary/ 3.0T 1.6T 1.5T 53% /home/gary
> >
> > $ df -h .snapshot/nightly.1/.configfiles
> > Filesystem Size Used Avail Use% Mounted on
> > fserver1b:/vol/users/gary/ 538G 270G 269G 51% /home/gary
> >
> > The file systems have the same names, but different stats.
> >
> > I've asked one of our IT guys to explain that to me.
> >
> > It remains, though, that that "feature" of vimdiff is still causing
> > me difficulty. I haven't looked yet at the code that Christian
> > pointed me to, but it seems that if vimdiff is going to try for some
> > sort of optimization by checking inode numbers, it ought to check
> > file systems as well.
>
> I haven't figured out how to distinguish the two file systems. The
> stat command indicates that the device numbers (%d) are the same,
>
> $ stat --format="%d %i %m %n" .snapshot/nightly.1/.configfiles/profile.common .configfiles/profile.common
> 37 14988947 /home/gary .snapshot/nightly.1/.configfiles/profile.common
> 37 14988947 /home/gary .configfiles/profile.common
>
> and that the file system IDs (%i) are the same,
>
> $ stat -f --format="%i %b %n" .snapshot/nightly.1/.configfiles/profile.common .configfiles/profile.common
> 0 17616077 .snapshot/nightly.1/.configfiles/profile.common
> 0 99824436 .configfiles/profile.common
>
> I included the total data blocks in the file systems (%b) in the
> second result to help confirm that the file systems are indeed
> different.
I had a chat with our IT guy. It turns out that our short-term
backup system, the one that periodically saves files to the
~/.snapshot directory, uses its own file system (perhaps a database
made to look like a file system) that preserves the inode numbers of
backed up files, as you can see in this output of ls.
$ ls -li .configfiles/profile.common .snapshot/*/.configfiles/profile.common
14988947 -rwx------ 1 gary gary 2269 Jul 9 15:00 .configfiles/profile.common
14988947 -rwx------ 1 gary gary 2269 Jul 9 15:00 .snapshot/hourly.0/.configfiles/profile.common
14988947 -rwx------ 1 gary gary 2269 Jul 9 15:00 .snapshot/hourly.1/.configfiles/profile.common
14988947 -rwx------ 1 gary gary 2269 Jul 9 15:00 .snapshot/hourly.2/.configfiles/profile.common
14988947 -rwx------ 1 gary gary 2269 Jul 9 15:00 .snapshot/hourly.3/.configfiles/profile.common
14988947 -rwx------ 1 gary gary 3676 Jul 9 11:57 .snapshot/hourly.4/.configfiles/profile.common
14988947 -rwx------ 1 gary gary 2992 Jul 7 10:07 .snapshot/hourly.5/.configfiles/profile.common
14988947 -rwx------ 1 gary gary 2269 Jul 9 15:00 .snapshot/nightly.0/.configfiles/profile.common
14988947 -rwx------ 1 gary gary 2992 Jul 7 10:07 .snapshot/nightly.1/.configfiles/profile.common
I also browsed through the Vim code for "inode". It appears that
Vim uses the inode number and the device number whenever it can to
determine whether two files are the same.
It would agree that if the inode numbers of two files are different,
it is safe to conclude that the files are different. However, as
observed here and as noted at lines 4639 and 4670 of memline.c, it
is not safe to assume that if the inode numbers of two files are
equal, the files are equal. It might be better if another test was
used to verify whether two files having the same inode numbers are
actually the same. This is done anyway on file systems without
inodes.
On the other hand, a file system such as we're using for backups
seems pretty unusual, and equal inode numbers over network file
systems is also pretty rare. Is this problem worth fixing? Would a
patch even be considered? Or should I just resort to workarounds
for the few times I have to recover part of a file?
Regards,
Gary
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