Fabiano Rosas <[email protected]> writes:
> We're about to enable the use of O_DIRECT in the migration code and
> due to the alignment restrictions imposed by filesystems we need to
> make sure the flag is only used when doing aligned IO.
>
> The migration will do parallel IO to different regions of a file, so
> we need to use more than one file descriptor. Those cannot be obtained
> by duplicating (dup()) since duplicated file descriptors share the
> file status flags, including O_DIRECT. If one migration channel does
> unaligned IO while another sets O_DIRECT to do aligned IO, the
> filesystem would fail the unaligned operation.
>
> The add-fd QMP command along with the fdset code are specifically
> designed to allow the user to pass a set of file descriptors with
> different access flags into QEMU to be later fetched by code that
> needs to alternate between those flags when doing IO.
>
> Extend the fdset matching function to behave the same with the
> O_DIRECT flag.
>
> Signed-off-by: Fabiano Rosas <[email protected]>
> ---
> monitor/fds.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/monitor/fds.c b/monitor/fds.c
> index 9a28e4b72b..42bf3eb982 100644
> --- a/monitor/fds.c
> +++ b/monitor/fds.c
> @@ -413,6 +413,12 @@ static bool monitor_fdset_flags_match(int flags, int
> fd_flags)
static bool monitor_fdset_flags_match(int flags, int fd_flags)
{
bool match = false;
> if ((flags & O_ACCMODE) == (fd_flags & O_ACCMODE)) {
> match = true;
> +
> +#ifdef O_DIRECT
> + if ((flags & O_DIRECT) != (fd_flags & O_DIRECT)) {
> + match = false;
> + }
> +#endif
> }
>
> return match;
}
I'd prefer something like
static bool monitor_fdset_flags_match(int flags, int fd_flags)
{
#ifdef O_DIRECT
if ((flags & O_DIRECT) != (fd_flags & O_DIRECT)) {
return false;
}
#endif
if ((flags & O_ACCMODE) != (fd_flags & O_ACCMODE)) {
return false;
}
return true;
}
