[musl] about getpwent functions family

[musl] about getpwent functions family

[Sebastien Marie]

Hi,

I am using alpine linux (which is using musl libc) and I am trying to
build xen-api [1].

xen-api is using getpwent_r (and getspent_r but let's focus on
getpwent_r) function in unixpwd [2], a simple C library with OCaml
bindings to support updating Unix account passwords in /etc/passwd and
/etc/shadow.

I am looking for rational or previous discussion about inclusion or not
of such GNU extension functions in musl.

fgetpwent and putpwent, which are also GNU extension, are already
present.

If there is no objection, I would look to provide patches for adding
getpwent_r() and/or fgetpwent_r() (and {,f}getspent_r counterpart).

Thanks.
-- 
Sebastien Marie

[1] https://github.com/xapi-project/xen-api
[2] https://github.com/xapi-project/xen-api/tree/master/unixpwd

Re: [musl] about getpwent functions family

[A. Wilcox]

On Oct 29, 2025, at 2:44 AM,
Sebastien Marie <semarie@kapouay.eu.org> wrote:
> 
> Hi,
> 
> I am using alpine linux (which is using musl libc) and I am trying to
> build xen-api [1].
> 
> xen-api is using getpwent_r (and getspent_r but let's focus on
> getpwent_r) function in unixpwd [2], a simple C library with OCaml
> bindings to support updating Unix account passwords in /etc/passwd and
> /etc/shadow.
> 
> I am looking for rational or previous discussion about inclusion or not
> of such GNU extension functions in musl.
> 
> fgetpwent and putpwent, which are also GNU extension, are already
> present.
> 
> If there is no objection, I would look to provide patches for adding
> getpwent_r() and/or fgetpwent_r() (and {,f}getspent_r counterpart).
> 
> Thanks.
> -- 
> Sebastien Marie
> 
> [1] https://github.com/xapi-project/xen-api
> [2] https://github.com/xapi-project/xen-api/tree/master/unixpwd

Hi Sebastien,

You may want to look in to libnsss[1], probably compiled with
`-DNSSS_DISABLE_SWITCH` so it only uses Unix files.

Best,
-Anna

[1]: https://skarnet.org/software/nsss/libnsss/index.html

—
Anna Wilcox (she/her)
SW Engineering: C++/Rust, DevOps, POSIX, Py/Ruby
Wilcox Technologies Inc.

Re: [musl] about getpwent functions family

[Rich Felker]

On Wed, Oct 29, 2025 at 08:44:24AM +0100, Sebastien Marie wrote:
> Hi,
> 
> I am using alpine linux (which is using musl libc) and I am trying to
> build xen-api [1].
> 
> xen-api is using getpwent_r (and getspent_r but let's focus on
> getpwent_r) function in unixpwd [2], a simple C library with OCaml
> bindings to support updating Unix account passwords in /etc/passwd and
> /etc/shadow.
> 
> I am looking for rational or previous discussion about inclusion or not
> of such GNU extension functions in musl.
> 
> fgetpwent and putpwent, which are also GNU extension, are already
> present.
> 
> If there is no objection, I would look to provide patches for adding
> getpwent_r() and/or fgetpwent_r() (and {,f}getspent_r counterpart).

The reason there's no getpwent_r is that it does nothing to solve the
problem with normal getpwent: it's still non-thread-safe and
non-library-safe, because it iterator it uses is global state. All it
does is give you the strictly-worse klunky buffer handling, but still
with the need to use locking.

fgetpwent_r solves this, but it doesn't abstract the source of
records. There's no interface to setup or tear down iterators; it
works directly on FILE* and only supports reading records from a
classic passwd file.

Rich

Re: [musl] about getpwent functions family

[Demi Marie Obenour]

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On 10/29/25 04:34, A. Wilcox wrote:
> On Oct 29, 2025, at 2:44 AM,
> Sebastien Marie <semarie@kapouay.eu.org> wrote:
>>
>> Hi,
>>
>> I am using alpine linux (which is using musl libc) and I am trying to
>> build xen-api [1].
>>
>> xen-api is using getpwent_r (and getspent_r but let's focus on
>> getpwent_r) function in unixpwd [2], a simple C library with OCaml
>> bindings to support updating Unix account passwords in /etc/passwd and
>> /etc/shadow.
>>
>> I am looking for rational or previous discussion about inclusion or not
>> of such GNU extension functions in musl.
>>
>> fgetpwent and putpwent, which are also GNU extension, are already
>> present.
>>
>> If there is no objection, I would look to provide patches for adding
>> getpwent_r() and/or fgetpwent_r() (and {,f}getspent_r counterpart).
>>
>> Thanks.
>> -- 
>> Sebastien Marie
>>
>> [1] https://github.com/xapi-project/xen-api
>> [2] https://github.com/xapi-project/xen-api/tree/master/unixpwd
> 
> Hi Sebastien,
> 
> You may want to look in to libnsss[1], probably compiled with
> `-DNSSS_DISABLE_SWITCH` so it only uses Unix files.
> 
> Best,
> -Anna
> 
> [1]: https://skarnet.org/software/nsss/libnsss/index.html

I recommend spawning a subprocess instead.
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)

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