On Thu, Nov 07, 2024 at 03:56:09PM -0800, Joanne Koong wrote:
> Add a new mapping flag AS_WRITEBACK_MAY_BLOCK which filesystems may set
> to indicate that writeback operations may block or take an indeterminate
> amount of time to complete. Extra caution should be taken when waiting
> on writeback for folios belonging to mappings where this flag is set.
>
> Signed-off-by: Joanne Koong <joannelkoong@xxxxxxxxx>
> ---
> include/linux/pagemap.h | 11 +++++++++++
> 1 file changed, 11 insertions(+)
>
> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> index 68a5f1ff3301..eb5a7837e142 100644
> --- a/include/linux/pagemap.h
> +++ b/include/linux/pagemap.h
> @@ -210,6 +210,7 @@ enum mapping_flags {
> AS_STABLE_WRITES = 7, /* must wait for writeback before modifying
> folio contents */
> AS_INACCESSIBLE = 8, /* Do not attempt direct R/W access to the mapping */
> + AS_WRITEBACK_MAY_BLOCK = 9, /* Use caution when waiting on writeback */
To me 'may block' does not feel right. For example in reclaim code,
folio_wait_writeback() can get blocked and that is fine. However with
non-privileged fuse involved, there are security concerns. Somehow 'may
block' does not convey that. Anyways, I am not really pushing back but
I think there is a need for better name here.
> /* Bits 16-25 are used for FOLIO_ORDER */
> AS_FOLIO_ORDER_BITS = 5,
> AS_FOLIO_ORDER_MIN = 16,
> @@ -335,6 +336,16 @@ static inline bool mapping_inaccessible(struct address_space *mapping)
> return test_bit(AS_INACCESSIBLE, &mapping->flags);
> }
>
> +static inline void mapping_set_writeback_may_block(struct address_space *mapping)
> +{
> + set_bit(AS_WRITEBACK_MAY_BLOCK, &mapping->flags);
> +}
> +
> +static inline bool mapping_writeback_may_block(struct address_space *mapping)
> +{
> + return test_bit(AS_WRITEBACK_MAY_BLOCK, &mapping->flags);
> +}
> +
> static inline gfp_t mapping_gfp_mask(struct address_space * mapping)
> {
> return mapping->gfp_mask;
> --
> 2.43.5
>
