Bug 199806

Summary: [libc] Add a new option letter "l" to make fopen() use O_SHLOCK or O_EXLOCK when calling open()
Product: Base System Reporter: jau
Component: kernAssignee: freebsd-bugs mailing list <bugs>
Status: New ---    
Severity: Affects Some People Keywords: patch
Priority: ---    
Version: CURRENT   
Hardware: Any   
OS: Any   
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A patch to add the proposed new option letter to fopen() none

Description jau 2015-04-30 11:25:53 UTC
Created attachment 156144 [details]
A patch to add the proposed new option letter to fopen()

This is a change proposal.

Since FreeBSD already has the open() flags O_SHLOCK and O_EXLOCK
it would make sense for the same feature to be also available when
calling fopen(). So, I propose adding a new option letter "l" to
force fopen() to add the suitable one of these locking flags when
calling open(), O_SHLOCK for "r" and O_EXLOCK for "w", "r+", etc.

Such an extension is of course non-standard, but when code portability
is not a big issue such an extension would make FreeBSD specific code
easier to read and write, and maybe also a bit more robust while avoiding
the need to go the extra mille passum to call fileno() and flock() later.

From my point of view writing something like...

fp = fopen("whateverfile", "wb+lex");

... is a pretty neat idea. Either I get a handle to a completely
new file with the exclusive lock applied, and it will not be left
open after an exec*() call, or I get a NULL.

Obviously the same change applies to 10.1 as well, if the merits of
this idea are accepted.