Re: RFC: Make dh_makeshlibs auto-detect udebs in common cases

[Niels Thykier <niels@thykier.net>]

Cyril Brulebois:
> Hi,
> 
> Niels Thykier <niels@thykier.net> (2019-02-24):
>> (Please CC me on replies per mail).
> 
> (Done.)
> 
>> I am seeing feedback on a PoC patch for dh_makeshlibs to have it
>> auto-detect udebs in the common case, where the udeb has the same name
>> as the deb followed by the suffix "-udeb".  AFAICT, this will make
>> --add-udeb obsolete in many cases as many udebs follow the previous
>> mentioned naming convention.
>>
>> The patch is available at [SALSA].  Please let me know what you think
>> about it.
>>
>> Thanks,
>> ~Niels
>>
>> [SALSA]: https://salsa.debian.org/debian/debhelper/merge_requests/21
> 
> Did you test rebuilding packages using that option against said
> debhelper, and were the results identical?
> 


Thanks for the feedback. :)

I have tested this and they do.


Test method: I have verified this against systemd at git master[1] using
the following three variants/builds:

 * Vanilla debhelper/12.2.3 with explicit --add-udeb
 * Patched debhelper/12.2.3 with explicit --add-udeb
 * Patched debhelper/12.2.3 dropping the "dh_makeshlibs -plibudev1 \
   --add-udeb=libudev1-udeb [...]" line[2]

All three generate identical results (i.e. bit-for-bit identical
debs/udebs)[3].

> Slightly worried by people possibly blindly dropping --add-udeb and not
> checking what happens to their packages. Would be nice to double-check
> up-front that everything works as intended.
> 
> 
> Cheers,
> 

I will never be able to make code that works all the time given the
premise that people "blindly" apply changes.  However, it is not my goal
either. The goal for this change is to simplify udeb handling to remove
one papercut /in the common case/ for udeb packages in two forms:

 1) Packages that need to add a new udeb will have one less step to
    worry about when they follow the naming convention for udebs.

 2) /Some/ existing udeb producing packages will be able to drop their
    manual overrides (assuming they follow this convention as well).
    An example of a package that would benefit is bind9, where we can
    remove about 11 lines[4].

While most packages seem follow the convention, there are exceptions.
As an example, I spotted fontconfig[5] which will not benefit from this
change.  Instead, it (and other exceptions) will have to keep --add-udeb.

Thanks,
~Niels


[1] Being pedantic, I manually disabling lto and skipped tested to speed
up the build.  But neither of those changes affects what dh_makeshlibs
would do.

[2] I.e. the udeb is now handled by the "dh_makeshlibs
--remaining-packages" line two lines further down.

[3]
> $ sha256sum ../dh-udeb-*patched-*/* | perl -p -e 's@ [.][.]/.*/@@' | sort  | uniq -c
>       3 038b3ed72cf8ea4e6d0053816ab30df4aa144c25424f86fbe2e8dd354fac8b55 systemd-journal-remote-dbgsym_241-6_amd64.deb
>       3 1cbf500fadaf90186087f4a5fc6e8c4fe60862e340b11a99e4daca6e4e2b10b2 systemd-coredump_241-6_amd64.deb
>       3 2aa7870a61ce402c09067fdfc56adb327b59ab1998201e526af68501a69163ba systemd-coredump-dbgsym_241-6_amd64.deb
>       3 2f1ab51bbb4cc228d1c1f3d289446873edcf48d6278031d70b455fc51513e4bd udev-udeb_241-6_amd64.udeb
>       3 46b2e60fdf18bca7a1e4fd8145fdd3e153d44fb441de12a997a4ca157e8faed8 systemd_241-6_amd64.deb
>       3 48675c51db2a9b27dcdedf869fbe32e59a1f24c322ceba52b7c79dde72aa4b10 libudev1_241-6_amd64.deb
>       3 49e8ab46e19ea8c1f430956144363dc9769c301f99ce0a51aa7ada7b9382d380 systemd-tests_241-6_amd64.deb
>       3 4f0147d49c12afb5672bfcaa6b5b8dfa3cb7b09ad8cccc1f5bb6416414f9b9c1 udev_241-6_amd64.deb
>       3 53489f3e9fa8839d0b93bc3316d0c09cb7e98ff51424d7961877822923b22a3d libudev1-dbgsym_241-6_amd64.deb
>       3 62f924f1e2575f58305b3a5d5937ee7c92ebce3eb4195252b17d77ee72955126 udev-dbgsym_241-6_amd64.deb
>       3 67a1bf0f20d8e2a26c711434b9697fc52eb7798e1931a2401dac82a91db3cc45 systemd-sysv_241-6_amd64.deb
>       3 6a44c6584d6c20bed06a50b5f6ebae21947e0c5ed879913a467d3e245c85ee0c systemd-tests-dbgsym_241-6_amd64.deb
>       3 925a78b13a78af8793ac6961bb6c8d48efa9dc083e4b07e7b773ff1b7512c3c2 systemd-journal-remote_241-6_amd64.deb
>       3 9cc85ddf88adf862d32e81016f0ffcfe1abedee09f33b9463b7e3d35a1df99c2 systemd-container_241-6_amd64.deb
>       3 9d26934e2223059e9be51d3488bfaafec8ed4c75cdce4721a9075f74c893b95a libsystemd0-dbgsym_241-6_amd64.deb
>       3 9e80822a057401bcf33248d0d2963b72ee5410db22f103f35769207298e9cbc0 libsystemd-dev_241-6_amd64.deb
>       3 bd4359c7318613759873b519dc4b33c8f6d7bc51549181599f47d2ea6975d27b libnss-systemd_241-6_amd64.deb
>       3 be4235e2f121f81af37d177b02be6d5997e0dfaeaa4dbd89e21f820988c4e136 libnss-systemd-dbgsym_241-6_amd64.deb
>       3 be5ce8fdbcd39f09e98da8702591cf809e051a4f6e1eabce4e16f78388b2c08d systemd-container-dbgsym_241-6_amd64.deb
>       3 c18217606b58a86679f9f861bb4c1ef0a25e61135e3c1415dc848c8e4360b5fa libudev1-udeb_241-6_amd64.udeb
>       3 d76f4486969095902d707054e8831ce426f944cfdfca2d60f71274d760ea69f3 libpam-systemd-dbgsym_241-6_amd64.deb
>       3 d7ad01e09c3774300f5efad1b1f1cec9a14a2a25d53ee1f5ded8074fbf943f01 systemd-dbgsym_241-6_amd64.deb
>       3 dbf2f5e8d790e10544b54a3690af4ccd621692f07ad4893e1cca9664187d8cad libudev-dev_241-6_amd64.deb
>       3 e00e105f6b28fedeb0087d7f5f19ef9eb805dc5f71ae1a26f6cbd0589968aafb libsystemd0_241-6_amd64.deb
>       3 e7879ad9a7d5987de4025abf20c7cd02bd6e8eff96ae10efcf0a4137f767c014 libpam-systemd_241-6_amd64.deb


[4] The entire override_dh_makeshlibs target in bind9/1:9.11.5.P4+dfsg-5.1.

https://sources.debian.org/src/bind9/1:9.11.5.P4+dfsg-5.1/debian/rules/#L163-L174

[5] fontconfig/2.13.1-2 contains the following:

"""
override_dh_makeshlibs:
    dh_makeshlibs -plibfontconfig1 -V"libfontconfig1 (>= 2.13)" \
      --add-udeb="fontconfig-udeb" -- -c4
"""

(editorial note: I realigned it and added a backslash continuation to
readability in the mail)