On Sat, Mar 19, 2022 at 12:28:31AM -0600, Jane Chu wrote:
> Introduce DAX_RECOVERY flag to dax_direct_access(). The flag is
> not set by default in dax_direct_access() such that the helper
> does not translate a pmem range to kernel virtual address if the
> range contains uncorrectable errors. When the flag is set,
> the helper ignores the UEs and return kernel virtual adderss so
> that the caller may get on with data recovery via write.
This DAX_RECOVERY doesn't actually seem to be used anywhere here or
in the subsequent patches. Did I miss something?
> Also introduce a new dev_pagemap_ops .recovery_write function.
> The function is applicable to FSDAX device only. The device
> page backend driver provides .recovery_write function if the
> device has underlying mechanism to clear the uncorrectable
> errors on the fly.
Why is this not in struct dax_operations?
>
> +size_t dax_recovery_write(struct dax_device *dax_dev, pgoff_t pgoff,
> + void *addr, size_t bytes, struct iov_iter *iter)
> +{
> + struct dev_pagemap *pgmap = dax_dev->pgmap;
> +
> + if (!pgmap || !pgmap->ops->recovery_write)
> + return -EIO;
> + return pgmap->ops->recovery_write(pgmap, pgoff, addr, bytes,
> + (void *)iter);
No need to cast a type pointer to a void pointer. But more importantly
losing the type information here and passing it as void seems very
wrong.
> +static size_t pmem_recovery_write(struct dev_pagemap *pgmap, pgoff_t pgoff,
> + void *addr, size_t bytes, void *iter)
> +{
> + struct pmem_device *pmem = pgmap->owner;
> +
> + dev_warn(pmem->bb.dev, "%s: not yet implemented\n", __func__);
> +
> + /* XXX more later */
> + return 0;
> +}
This shuld not be added here - the core code can cope with a NULL
method just fine.
> + recov = 0;
> + flags = 0;
> + nrpg = PHYS_PFN(size);
Please spell out the words. The recovery flag can also be
a bool to make the code more readable.
> + map_len = dax_direct_access(dax_dev, pgoff, nrpg, flags,
> + &kaddr, NULL);
> + if ((map_len == -EIO) && (iov_iter_rw(iter) == WRITE)) {
No need for the inner braces.
> + flags |= DAX_RECOVERY;
> + map_len = dax_direct_access(dax_dev, pgoff, nrpg,
> + flags, &kaddr, NULL);
And noneed for the flags variable at all really.
> xfer = dax_copy_from_iter(dax_dev, pgoff, kaddr,
> map_len, iter);
> else
> @@ -1271,6 +1286,11 @@ static loff_t dax_iomap_iter(const struct iomap_iter *iomi,
> length -= xfer;
> done += xfer;
>
> + if (recov && (xfer == (ssize_t) -EIO)) {
> + pr_warn("dax_recovery_write failed\n");
> + ret = -EIO;
> + break;
And no, we can't just use an unsigned variable to communicate a
negative error code.
