On 05/06/2024 09:30, Christoph Hellwig wrote:
Highlevel question: in a lot of the discussions we've used the
term "untorn writes" instead, which feels better than atomic to
me as atomic is a highly overloaded term. Should we switch the
naming to that?
I have no strong attachment to that name (atomic).
For both SCSI and NVMe, it's an "atomic" feature and I was basing the
naming on that.
We could have RWF_NOTEARS or RWF_UNTEARABLE_WRITE or RWF_UNTEARABLE or
RWF_UNTORN or similar. Any preference?
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 0283cf366c2a..6cb67882bcfd 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -45,6 +45,7 @@
#include <linux/slab.h>
#include <linux/maple_tree.h>
#include <linux/rw_hint.h>
+#include <linux/uio.h>
fs.h is included almost everywhere, so if we can avoid pulling in
even more dependencies that would be great.
It seems like it is pulled in just for this helper:
right
+static inline
+bool generic_atomic_write_valid(loff_t pos, struct iov_iter *iter)
+{
+ size_t len = iov_iter_count(iter);
+
+ if (!iter_is_ubuf(iter))
+ return false;
+
+ if (!is_power_of_2(len))
+ return false;
+
+ if (!IS_ALIGNED(pos, len))
+ return false;
+
+ return true;
+}
should that just go to uio.h instead, or move out of line?
ok, I am not sure about moving to uio.h, but I'll try to do something
about this issue
Also the return type formatting is wrong, the two normal styles are
either:
static inline bool generic_atomic_write_valid(loff_t pos,
struct iov_iter *iter)
or:
static inline bool
generic_atomic_write_valid(loff_t pos, struct iov_iter *iter)
(and while I'm at nitpicking, passing the pos before the iter
feels weird)
generally pos is first and then len (which iter provides) when a
function accepts position and length, but then iter is the "larger" arg,
and normally they go first. Anyway I don't mind changing that as you
suggest.
Last but not least: if READ/WRITE is passed to kiocb_set_rw_flags,
it should probably set IOCB_WRITE as well? That might be a worthwile
prep patch on it's own.
For io_uring/rw.c, we have io_write() -> io_rw_init_file(..., WRITE),
and then later we set IOCB_WRITE, so would be neat to use there. But
then do_iter_readv_writev() does not set IOCB_WRITE - I can't imagine
that setting IOCB_WRITE would do any harm there. I see a similar change
in
https://lore.kernel.org/linux-fsdevel/167391048988.2311931.1567396746365286847.stgit@xxxxxxxxxxxxxxxxxxxxxx/
AFAICS, setting IOCB_WRITE is quite inconsistent. From browsing through
fsdevel on lore, there was some history in trying to use IOCB_WRITE
always instead of iov_iter direction. Any idea what happened to that?
I'm just getting the feeling that setting IOCB_WRITE in
kiocb_set_rw_flags() is a small part - and maybe counter productive - of
a larger job of fixing IOCB_WRITE usage.
Thanks,
John
