[RFC v1] man/man2/close.2: CAVEATS: Document divergence from POSIX.1-2024

[The 8472]

On 26/01/2026 13:15, Jan Kara wrote:
> On Sun 25-01-26 10:37:01, Zack Weinberg wrote:
>> On Sat, Jan 24, 2026, at 4:57 PM, The 8472 wrote:
>>
>>>>       [QUERY: Do delayed errors ever happen in any of these situations?
>>>>
>>>>          - The fd is not the last reference to the open file description
>>>>
>>>>          - The OFD was opened with O_RDONLY
>>>>
>>>>          - The OFD was opened with O_RDWR but has never actually
>>>>            been written to
>>>>
>>>>          - No data has been written to the OFD since the last call to
>>>>            fsync() for that OFD
>>>>
>>>>          - No data has been written to the OFD since the last call to
>>>>            fdatasync() for that OFD
>>>>
>>>>          If we can give some guidance about when people don’t need to
>>>>          worry about delayed errors, it would be helpful.]
>>
>> In particular, I really hope delayed errors *aren’t* ever reported
>> when you close a file descriptor that *isn’t* the last reference
>> to its open file description, because the thread-safe way to close
>> stdout without losing write errors[2] depends on that not happening.
> 
> So I've checked and in Linux ->flush callback for the file is called
> whenever you close a file descriptor (regardless whether there are other
> file descriptors pointing to the same file description) so it's upto
> filesystem implementation what it decides to do and which error it will
> return... Checking the implementations e.g. FUSE and NFS *will* return
> delayed writeback errors on *first* descriptor close even if there are
> other still open descriptors for the description AFAICS.
Regarding the "first", does that mean the errors only get delivered once?
I.e. if a concurrent fork/exec happens for process spawning and the fork-child
closes the file descriptors then this closing may basically receive the errors
and the parent will not see them (unless additional errors happen)?
Or if _any_ part of the program dups the descriptor and then closes it without
reporting errors then all uses of those descriptor must consider error delivery
on close to be unreliable?