Re: master fails to build on FreeBSD when ACL support is on

[Paul Eggert <eggert@cs.ucla.edu>]

On 01/22/2018 09:41 AM, Eli Zaretskii wrote:
> Why do we need to inform the callers that ACL setting failed

Because they invoked copy-file with a non-nil preserve-permissions flag, 
and copy-file cannot preserve the permissions as requested. It's the 
same reason copy-file signals an error when invoked with a non-nil 
keep-time flag and when it cannot keep the time on the output file. If 
copy-file did not report an error, users would be lulled into thinking 
that the destination has the same permissions as the source when 
copy-file succeeds, even though that's not the case.

There is some precedent for ignoring failure, as copy-file does ignore 
chown failure when the preserve-uid-gid flag is used. However, this 
behavior is documented as a specific exception to the general rule that 
copy-file signals failures.

One way to move forward would be to change copy-file to have a three-way 
result, as set-file-acl does. That is, it could return t if successful, 
nil if mildly unsuccessful, and signal an error if severely 
unsuccessful. Failure to preserve UID and GID would be considered mild. 
Perhaps failure to preserve permissions could be considered mild, too, 
since it's no more security-relevant than UID failure is.