lib/posix-sysinfo: Provide _SC_GETPW_R_SIZE_MAX

[andreittr]

Description of changes

Calling code expects sysconf(_SC_GETPW_R_SIZE_MAX) to be either -1 or a non-zero value for an initial buffer size. The previous default value of 0 is outside of specifications and can cause unintended behavior. This change makes sysconf(_SC_GETPW_R_SIZE_MAX) return -1.

See man 3 getpwuid for the specifications for sysconf(_SC_GETPW_R_SIZE_MAX).

Prerequisite checklist

• Read the contribution guidelines regarding submitting new changes to the project;
• Tested your changes against relevant architectures and platforms;
• Ran the checkpatch.uk on your commit series before opening this PR;
• Updated relevant documentation.

Base target

• Architecture(s): N/A
• Platform(s): N/A
• Application(s): N/A

Additional configuration

CONFIG_LIBPOSIX_USER=y and CONFIG_LIBPOSIX_SYSINFO=y.

[unikraft-bot]

✅ Checkpatch passed

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SHA	commit	checkpatch
5eecf9c	lib/posix-sysinfo: Provide _SC_GETPW_R_SIZE_MAX	✅

[StefanJum]

@andreittr we should define _SC_GETPW_R_SIZE_MAX in nolibc/include/unistd.h, otherwise the build fails when using nolibc.

[andreittr]

Update: added define of _SC_GETPW_R_SIZE_MAX to nolibc.

[StefanJum]

Looks good now. I'll add the tag after @John-Ted and @razvand take a look.

[razvand]

@John-Ted , please take a look, so I can then approve it and have it merged.

[John-Ted]

I'm trying to compile the helloworld app to print the sysconf value, but I cannot get it to compile. I have selected the 2 options in the config, and I included unistd.h. I get the following errors:

  CC      apphelloworld: main.o
/home/teodor/Documents/ac/unikraft/pr_reviews/rev1/apps/app-helloworld/main.c: In function ‘main’:
/home/teodor/Documents/ac/unikraft/pr_reviews/rev1/apps/app-helloworld/main.c:34:37: warning: implicit declaration of function ‘sysconf’; did you mean ‘sscanf’? [-Wimplicit-function-declaration]
   34 |         printf("Hello world %d!\n", sysconf(_SC_GETPW_R_SIZE_MAX));
      |                                     ^~~~~~~
      |                                     sscanf
/home/teodor/Documents/ac/unikraft/pr_reviews/rev1/apps/app-helloworld/main.c:34:45: error: ‘_SC_GETPW_R_SIZE_MAX’ undeclared (first use in this function)
   34 |         printf("Hello world %d!\n", sysconf(_SC_GETPW_R_SIZE_MAX));
      |                                             ^~~~~~~~~~~~~~~~~~~~
/home/teodor/Documents/ac/unikraft/pr_reviews/rev1/apps/app-helloworld/main.c:34:45: note: each undeclared identifier is reported only once for each function it appears in
make[3]: *** [/home/teodor/Documents/ac/unikraft/pr_reviews/rev1/apps/app-helloworld/.unikraft/unikraft/support/build/Makefile.build:27: /home/teodor/Documents/ac/unikraft/pr_reviews/rev1/apps/app-helloworld/build/apphelloworld/main.o] Error 1

config.txt
main.c.txt

[andreittr]

I'm trying to compile the helloworld app to print the sysconf value, but I cannot get it to compile. I have selected the 2 options in the config, and I included unistd.h. I get the following errors:

Whoops, seems sysconf is not declared in nolibc's unistd.h; will push a new commit with a fix.

[John-Ted]

Everything works fine now. Thanks!

Reviewed-by: Ioan-Teodor Teugea ioan_teodor.teugea@stud.acs.upb.ro

[razvand]

Approved-by: Razvan Deaconescu razvand@unikraft.io