[Buildroot] [Bug 15856] New: Using BR2_CONFIG= on a different file-system than O= (build outputs) fails with kconfig syncconfig error

[Buildroot] [Bug 15856] New: Using BR2_CONFIG= on a different file-system than O= (build outputs) fails with kconfig syncconfig error

[bugzilla]

https://bugs.busybox.net/show_bug.cgi?id=15856

            Bug ID: 15856
           Summary: Using BR2_CONFIG= on a different file-system than O=
                    (build outputs) fails with kconfig syncconfig error
           Product: buildroot
           Version: 2023.08.3
          Hardware: All
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P5
         Component: Other
          Assignee: unassigned@buildroot.uclibc.org
          Reporter: ciprian.craciun@gmail.com
                CC: buildroot@uclibc.org
  Target Milestone: ---

If one has BuildRoot sources checked out on a file-system, but uses a build
outputs folder on a different file-system (via `make O=...`) and one also
specifies `BR2_CONFIG` on the first file-system (the one holding the sources),
the `make syncconfig` target fails with an `*** Error during update of the
configuration.` error.

`strace`-ing the `conf syncconfig` invocation leads me to the following
conclusion:

* something in the build system (perhaps `kconfig`) creates temporary files in
the parent folder of the configuration file (the one specified via
`BR2_CONFIG`);

* but then it tries to move it inside the outputs folder with a simple `rename`
syscall`;

* this fails because the rename is cross mount points;

The output of `strace` (here `/mnt/.../sources` where the sources and the
config are is a different mount point than `/mnt/.../volatile` where the
outputs are):
~~~~
rename("/mnt/.../sources/buildroot/!custom/.tmpconfig.h",
"/mnt/.../volatile/buildroot/build/build/buildroot-config/autoconf.h") = -1
EXDEV (Invalid cross-device link)
~~~~

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[Buildroot] [Bug 15856] Using BR2_CONFIG= on a different file-system than O= (build outputs) fails with kconfig syncconfig error

[bugzilla]

https://bugs.busybox.net/show_bug.cgi?id=15856

Arnout Vandecappelle <arnout@mind.be> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |WONTFIX
             Status|NEW                         |RESOLVED

--- Comment #1 from Arnout Vandecappelle <arnout@mind.be> ---
> and one also specifies `BR2_CONFIG`

BR2_CONFIG is not something that is supposed to be overridden. It is supposed
to reside in the same location as the output directory.

We will not accept patches that fix this specific problem you have.

What is your use case for putting the configuration file outside of the output
directory? Perhaps we can find a better solution for this specific use case.
However, please discuss this on the mailing list [1] rather than in the bug
tracker.

[1] https://lists.buildroot.org/mailman/listinfo/buildroot

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