[PATCH] Change sync_file_range to be non-cancellable

[Szabolcs Nagy]

On 21/10/15 14:24, Florian Weimer wrote:
> On 10/21/2015 02:34 PM, Adhemerval Zanella wrote:
>> This patch changes the linux specific sync_file_range syscalls to be
>> non-cancellable.  The rationale is:
>>
>> 1. This is a Linux specific syscall that is not mentioned in POSIX
>>     cancellable entrypoints [1] and the standard states and implementation
>>     shall not introduce cancellation points into any other functions
>>     specified.
>
> It says that we must not make any function mentioned in POSIX
> cancellable.  We can certainly introduce our own functions which are
> cancellable and not port of POSIX.
>
> I think sync_file_range should be cancellable for consistency with fsync
> and fdatasync.
>

this is something musl might want too.

one ugliness is that cancellation is either guaranteed
to be acted upon or guaranteed not to, which is bad
for all cases when there is a fast path in libc that
avoids calling the blocking syscall.

e.g. sync_file_range is not a cancellation point now
if it returns ENOSYS in glibc.

> Florian
>