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charset="utf-8" Allow stacked devices to support atomic writes by aggregating the minimum capability of all bottom devices. Flag BLK_FEAT_ATOMIC_WRITES_STACKED is set for stacked devices which have been enabled to support atomic writes. Some things to note on the implementation: - For simplicity, all bottom devices must have same atomic write boundary value (if any) - The atomic write boundary must be a power-of-2 already, but this restriction could be relaxed. Furthermore, it is now required that the chunk sectors for a top device must be aligned with this boundary. - If a bottom device atomic write unit min/max are not aligned with the top device chunk sectors, the top device atomic write unit min/max are reduced to a value which works for the chunk sectors. Signed-off-by: John Garry Reviewed-by: Christoph Hellwig --- block/blk-settings.c | 115 +++++++++++++++++++++++++++++++++++++++++ include/linux/blkdev.h | 4 ++ 2 files changed, 119 insertions(+) diff --git a/block/blk-settings.c b/block/blk-settings.c index c5a753f980bf..8d3a9a55462e 100644 --- a/block/blk-settings.c +++ b/block/blk-settings.c @@ -496,6 +496,119 @@ static unsigned int blk_round_down_sectors(unsigned i= nt sectors, unsigned int lb return sectors; } =20 +/* Check if second and later bottom devices are compliant */ +static bool blk_stack_atomic_writes_tail(struct queue_limits *t, + struct queue_limits *b) +{ + /* We're not going to support different boundary sizes.. yet */ + if (t->atomic_write_hw_boundary !=3D b->atomic_write_hw_boundary) + return false; + + /* Can't support this */ + if (t->atomic_write_hw_unit_min > b->atomic_write_hw_unit_max) + return false; + + /* Or this */ + if (t->atomic_write_hw_unit_max < b->atomic_write_hw_unit_min) + return false; + + t->atomic_write_hw_max =3D min(t->atomic_write_hw_max, + b->atomic_write_hw_max); + t->atomic_write_hw_unit_min =3D max(t->atomic_write_hw_unit_min, + b->atomic_write_hw_unit_min); + t->atomic_write_hw_unit_max =3D min(t->atomic_write_hw_unit_max, + b->atomic_write_hw_unit_max); + return true; +} + +/* Check for valid boundary of first bottom device */ +static bool blk_stack_atomic_writes_boundary_head(struct queue_limits *t, + struct queue_limits *b) +{ + /* + * Ensure atomic write boundary is aligned with chunk sectors. Stacked + * devices store chunk sectors in t->io_min. + */ + if (b->atomic_write_hw_boundary > t->io_min && + b->atomic_write_hw_boundary % t->io_min) + return false; + if (t->io_min > b->atomic_write_hw_boundary && + t->io_min % b->atomic_write_hw_boundary) + return false; + + t->atomic_write_hw_boundary =3D b->atomic_write_hw_boundary; + return true; +} + + +/* Check stacking of first bottom device */ +static bool blk_stack_atomic_writes_head(struct queue_limits *t, + struct queue_limits *b) +{ + if (b->atomic_write_hw_boundary && + !blk_stack_atomic_writes_boundary_head(t, b)) + return false; + + if (t->io_min <=3D SECTOR_SIZE) { + /* No chunk sectors, so use bottom device values directly */ + t->atomic_write_hw_unit_max =3D b->atomic_write_hw_unit_max; + t->atomic_write_hw_unit_min =3D b->atomic_write_hw_unit_min; + t->atomic_write_hw_max =3D b->atomic_write_hw_max; + return true; + } + + /* + * Find values for limits which work for chunk size. + * b->atomic_write_hw_unit_{min, max} may not be aligned with chunk + * size (t->io_min), as chunk size is not restricted to a power-of-2. + * So we need to find highest power-of-2 which works for the chunk + * size. + * As an example scenario, we could have b->unit_max =3D 16K and + * t->io_min =3D 24K. For this case, reduce t->unit_max to a value + * aligned with both limits, i.e. 8K in this example. + */ + t->atomic_write_hw_unit_max =3D b->atomic_write_hw_unit_max; + while (t->io_min % t->atomic_write_hw_unit_max) + t->atomic_write_hw_unit_max /=3D 2; + + t->atomic_write_hw_unit_min =3D min(b->atomic_write_hw_unit_min, + t->atomic_write_hw_unit_max); + t->atomic_write_hw_max =3D min(b->atomic_write_hw_max, t->io_min); + + return true; +} + +static void blk_stack_atomic_writes_limits(struct queue_limits *t, + struct queue_limits *b) +{ + if (!(t->features & BLK_FEAT_ATOMIC_WRITES_STACKED)) + goto unsupported; + + if (!b->atomic_write_unit_min) + goto unsupported; + + /* + * If atomic_write_hw_max is set, we have already stacked 1x bottom + * device, so check for compliance. + */ + if (t->atomic_write_hw_max) { + if (!blk_stack_atomic_writes_tail(t, b)) + goto unsupported; + return; + } + + if (!blk_stack_atomic_writes_head(t, b)) + goto unsupported; + return; + +unsupported: + t->atomic_write_hw_max =3D 0; + t->atomic_write_hw_unit_max =3D 0; + t->atomic_write_hw_unit_min =3D 0; + t->atomic_write_hw_boundary =3D 0; + t->features &=3D ~BLK_FEAT_ATOMIC_WRITES_STACKED; +} + /** * blk_stack_limits - adjust queue_limits for stacked devices * @t: the stacking driver limits (top device) @@ -656,6 +769,8 @@ int blk_stack_limits(struct queue_limits *t, struct que= ue_limits *b, t->zone_write_granularity =3D 0; t->max_zone_append_sectors =3D 0; } + blk_stack_atomic_writes_limits(t, b); + return ret; } EXPORT_SYMBOL(blk_stack_limits); diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h index 7bfc877e159e..272e7cd03297 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -333,6 +333,10 @@ typedef unsigned int __bitwise blk_features_t; #define BLK_FEAT_RAID_PARTIAL_STRIPES_EXPENSIVE \ ((__force blk_features_t)(1u << 15)) =20 +/* stacked device can/does support atomic writes */ +#define BLK_FEAT_ATOMIC_WRITES_STACKED \ + ((__force blk_features_t)(1u << 16)) + /* * Flags automatically inherited when stacking limits. */ --=20 2.31.1