Package upgrades break if hardlinks got added

[Vogtinator]

The algorithm used for installing hardlinks does not handle the case where a package upgrade includes additional names for an inode. It iterates the list of files from the beginning until the end and only writes content and metadata for the last occurence of an inode.
For upgrades, there is no hardlink relationship though, the added file has a different inode. This means that the content and metadata are written only to the files from the old package.
As the file content didn't change, the other names for the inode verify successfully and are thus not written to, so neither recreated as hardlinks to the new file nor file content written into the inode.
Reproducer:

Name: pkg
Version: %{ver}
Release: 0
License: WTFPL
Summary: Package

%description
.

%install
mkdir -p %{buildroot}/usr
echo "content" > %{buildroot}/usr/file2
%if %{ver} == 1
ln %{buildroot}/usr/file2 %{buildroot}/usr/file1
%endif

%files
%if %{ver} == 1
/usr/file1
%endif
/usr/file2

To build:

rpmbuild -bb -D 'ver 0' pkg.spec
rpmbuild -bb -D 'ver 1' pkg.spec

To install:

localhost:~ # rpm -U pkg-0-0.x86_64.rpm
localhost:~ # ll /usr/file{1,2}
ls: cannot access '/usr/file1': No such file or directory
-rw-r--r-- 1 root root 8 Jun 22  2020 /usr/file2
localhost:~ # rpm -U pkg-1-0.x86_64.rpm
localhost:~ # ll /usr/file{1,2}
--w------- 1 root root 0 Jun 22 05:34 /usr/file1
-rw-r--r-- 1 root root 8 Jun 22  2020 /usr/file2

As you can see, /usr/file1 was created with wrong mode and no content. The two files do not share an inode. It works if the package is installed directly:

localhost:~ # rpm -e pkg
localhost:~ # rpm -U pkg-1-0.x86_64.rpm
localhost:~ # ll /usr/file{1,2}
-rw-r--r-- 2 root root 8 Jun 22  2020 /usr/file1
-rw-r--r-- 2 root root 8 Jun 22  2020 /usr/file2

[pmatilai]

With --force, if something breaks you get to keep the pieces. Is it reproducable without --force?

[Vogtinator]

Yes.

I only used --force so that I can use the same commands for install, upgrade and downgrade.

[Vogtinator]

I ran the commands again without --force and edited the post accordingly.

[pmatilai]

Ok, thanks for verifying.

Just FWIW, --oldpackage is the "appropriate" flag for downgrades, --force is the BFH usually best left in the toolshed 😁

[Vogtinator]

Just found out that this only happens with %_minimize_writes enabled, as otherwise even unchanged files are recreated correctly as hardlinks.

D: create     100644  2 (   0,   0)     0 /usr/file1;5ef086f0
D: touch      100644  2 (   0,   0)     8 /usr/file2

vs.

D: create     100644  2 (   0,   0)     0 /usr/file1;5ef09669
D: create     100644  2 (   0,   0)     8 /usr/file2;5ef09669

%_minimize_writes is the default for SSDs (and on openSUSE in general) though.

[pmatilai]

Ah... makes sense. Thanks for spotting that!

[pmatilai]

Thanks for reporting and the nice reproducer!

[Vogtinator]

Thanks for the quick fix!