[RFC] btrfs-progs: Support for musl libc (and perhaps also uclibc)

Commit Message

Merlijn Wajer Dec. 13, 2014, 2:35 p.m. UTC

Hi,

I've been experimenting with musl-libc Gentoo systems. I used the HEAD
of git://git.kernel.org/pub/scm/linux/kernel/git/kdave/btrfs-progs.git

I found that btrfs-progs does not compile with musl-libc, for a few reasons:

* It makes use of the private glibc __always_inline macro.

* Various headers that should be included are not included:
linux/limits.h and limits.h. (for XATTR_SIZE_MAX and PATH_MAX)

* backtrace() using execinfo.h is enabled by default; execinfo.h is
glibc-specific and thus does not work on other libc's. musl does not
support it, and I think uclibc also does not support it.

I have worked around the problems in the following way:

* Define __always_inline if __glibc__ is not defined. This is arguably
the most clean solution. It would be better to simply not use the
__always_inline macro (instead, use __attribute__) throughout
btrfs-progs, but I was not sure what the developers would prefer. This
is currently done in kerncompat.h, but you may want to move that to
another file.

* Include various headers where required.

* If __glibc__ is not defined, define BTRFS_DISABLE_BACKTRACE. Currently
the define magic happens in kerncompat, because that also where BTRFS
includes execinfo. Personally, I think it would make more sense to
always disable backtrace instead of enabling it by default -- but
perhaps in a testing phase, enabling it by default in the sensible choice.

Attached are the two patches generated with git format-patch. I am aware
that this may not be required format for submitting patches -- but
please give me some time to get used to the etiquette. :-)

Please let me know if musl-libc (or any other libc) is a supported
platform, and if so, if and how I can improve on said patches.

Regards,
Merlijn

Comments

David Sterba Dec. 17, 2014, 4:49 p.m. UTC | #1

On Sat, Dec 13, 2014 at 03:35:09PM +0100, Merlijn Wajer wrote:
[snip]

> Attached are the two patches generated with git format-patch. I am aware
> that this may not be required format for submitting patches -- but
> please give me some time to get used to the etiquette. :-)

Thanks, there are minor things that I won't bother to point out to
occasional contributors and fix them myself. The only formal requirement
is the Signed-off-by tag, you can find the description eg. here

http://lxr.free-electrons.com/source/Documentation/SubmittingPatches#L358

> Please let me know if musl-libc (or any other libc) is a supported
> platform, and if so, if and how I can improve on said patches.

I'm not aware of non-glibc users, but I don't see any problem to add
support for more libc implementations. However, I won't regularly verify
that it builds so it might break.

Seems that only standardized library calls are used in btrfs-progs so
any kind of support is probably going to be satisfied by #ifdefs.

Your patches are simple so I'll try to schedule them to some 3.18.x
update.
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Austin S. Hemmelgarn Dec. 17, 2014, 6:46 p.m. UTC | #2

On 2014-12-17 11:49, David Sterba wrote:
> On Sat, Dec 13, 2014 at 03:35:09PM +0100, Merlijn Wajer wrote:
> [snip]
>> Please let me know if musl-libc (or any other libc) is a supported
>> platform, and if so, if and how I can improve on said patches.
>
> I'm not aware of non-glibc users, but I don't see any problem to add
> support for more libc implementations. However, I won't regularly verify
> that it builds so it might break.
I know that buildroot has support for building btrfs-progs with uClibc, 
I don't know if they have any special patches for it though.  Although I 
haven't tried it myself, I think it is also possible to use buildroot 
with musl.

Patch

From 01d0bfe48dc78b66b6e86d4935d9b9d20194b135 Mon Sep 17 00:00:00 2001
From: Merlijn Wajer <[e-mail]>
Date: Sat, 13 Dec 2014 15:08:43 +0100
Subject: [PATCH 2/2] Disable backtrace and define __always_inline

Disable backtrace and define __always_inline when glibc is not used as
libc. This, together with some header changes allows btrfs-progs to
compile with musl-libc.
---
 kerncompat.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/kerncompat.h b/kerncompat.h
index 8afadc8..05823a7 100644
--- a/kerncompat.h
+++ b/kerncompat.h
@@ -29,6 +29,12 @@ 
 #include <stddef.h>
 #include <linux/types.h>
 #include <stdint.h>
+
+#ifndef __glibc__
+#define BTRFS_DISABLE_BACKTRACE
+#define __always_inline __inline __attribute__ ((__always_inline__))
+#endif
+
 #ifndef BTRFS_DISABLE_BACKTRACE
 #include <execinfo.h>
 #endif
-- 
2.0.4