Re: portability of fopen and 'e' (O_CLOEXEC) flag

[Tim Rühsen]

Hi Bruno,

On 11.05.20 18:37, Bruno Haible wrote:
> Hi Tim,
> 
>> i would like to ask for your expert knowledge.
>>
>> How to prevent file descriptor leaks in a multi-threaded application
>> that fork+exec. Quick answer is surely "use O_CLOEXEC" to close those
>> file descriptors on exec.
>>
>> But how does this work with fopen in a portable way ?
>> GNU libc has the 'e' flag for exactly this.
> 
> Yes [1].
> 
>> How about other non-GNU OSes / alternative C libraries ?
> 
> POSIX [2][3], macOS [4], FreeBSD [5], Solaris [6] don't support this 'e' flag.
> 
> How about using open() with O_CLOEXEC, and then fdopen()?

Thanks. Sure, this is possible. Doing so at dozens of places (or more)
asks for an implementation in gnulib :)

Several projects (most library code) could benefit. I currently think
about GnuTLS where we have to fix this in one or the other way. Updating
gnulib and adding 'e' to the fopen modes would be straight forward.

> 
> Bruno
> 
> [1] http://man7.org/linux/man-pages/man3/fopen.3.html
> [2] https://pubs.opengroup.org/onlinepubs/9699919799/functions/fopen.html
> [3] http://man7.org/linux/man-pages/man3/fopen.3p.html
> [4] 
> https://developer.apple.com/library/archive/documentation/System/Conceptual/ManPages_iPhoneOS/man3/fopen.3.html
> [5] 
> https://www.freebsd.org/cgi/man.cgi?query=fopen&sektion=3&apropos=0&manpath=freebsd
> [6] https://docs.oracle.com/cd/E36784_01/html/E36874/fopen-3c.html
> 
>

signature.asc
Description: OpenPGP digital signature