On Wed, Jul 08, 2020 at 03:22:51PM +0100, Matthew Wilcox wrote:
On Wed, Jul 08, 2020 at 06:28:05PM +0530, Kanchan Joshi wrote:
The last thing is about the flag used to trigger this processing. Will it be
fine to intoduce new flag (RWF_APPEND2 or RWF_APPEND_OFFSET)
instead of using RWF_APPEND?
New flag will do what RWF_APPEND does and will also return the
written-location (and therefore expects pointer setup in application).
I think it's simpler to understand if it's called RWF_INDIRECT_OFFSET
Then it'd look like:
+ rwf_t rwf = READ_ONCE(sqe->rw_flags);
...
- iocb->ki_pos = READ_ONCE(sqe->off);
+ if (rwf & RWF_INDIRECT_OFFSET) {
+ loff_t __user *loffp = u64_to_user_ptr(sqe->addr2);
+
+ if (get_user(iocb->ki_pos, loffp)
+ return -EFAULT;
+ iocb->ki_loffp = loffp;
+ } else {
+ iocb->ki_pos = READ_ONCE(sqe->off);
+ }
...
- ret = kiocb_set_rw_flags(kiocb, READ_ONCE(sqe->rw_flags));
+ ret = kiocb_set_rw_flags(kiocb, rwf);
It will sure go like this in io_uring, except I was thinking to use
io_kiocb rather than iocb for "loffp".
I am fine with RWF_INDIRECT_OFFSET, but wondering - whether to build
this over base-behavior offered by RWF_APPEND.
This is what I mean in code (I used RWF_APPEND2 here)-
static inline int kiocb_set_rw_flags(struct kiocb *ki, rwf_t flags)
ki->ki_flags |= (IOCB_DSYNC | IOCB_SYNC);
if (flags & RWF_APPEND)
ki->ki_flags |= IOCB_APPEND;
+ if (flags & RWF_APPEND2) {
+ /*
+ * RWF_APPEND2 is "file-append + return write-location"
+ * Use IOCB_APPEND for file-append, and new IOCB_ZONE_APPEND
+ * to return where write landed
+ */
+ ki->ki_flags |= IOCB_APPEND;
+ if (ki->ki_filp->f_mode & FMODE_ZONE_APPEND) /*revisit the need*/
+ ki->ki_flags |= IOCB_ZONE_APPEND;
+ }
+
