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block: add ability to flag write back caching on a device

Browse source 
Add an internal helper and flag for setting whether a queue has
write back caching, or write through (or none). Add a sysfs file
to show this as well, and make it changeable from user space.

This will replace the (awkward) blk_queue_flush() interface that
drivers currently use to inform the block layer of write cache state
and capabilities.

Signed-off-by: Jens Axboe <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
This commit is contained in:
Jens Axboe 2016-04-12 12:32:46 -06:00
commit 93e9d8e836
4 changed files with 77 additions and 0 deletions
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39
block/blk-sysfs.c
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@ -347,6 +347,38 @@ static ssize_t queue_poll_store(struct request_queue *q, const char *page,
return ret;
}
static ssize_t queue_wc_show(struct request_queue *q, char *page)
{
if (test_bit(QUEUE_FLAG_WC, &q->queue_flags))
return sprintf(page, "write back\n");
return sprintf(page, "write through\n");
}
static ssize_t queue_wc_store(struct request_queue *q, const char *page,
size_t count)
{
int set = -1;
if (!strncmp(page, "write back", 10))
set = 1;
else if (!strncmp(page, "write through", 13) ||
!strncmp(page, "none", 4))
set = 0;
if (set == -1)
return -EINVAL;
spin_lock_irq(q->queue_lock);
if (set)
queue_flag_set(QUEUE_FLAG_WC, q);
else
queue_flag_clear(QUEUE_FLAG_WC, q);
spin_unlock_irq(q->queue_lock);
return count;
}
static struct queue_sysfs_entry queue_requests_entry = {
.attr = {.name = "nr_requests", .mode = S_IRUGO | S_IWUSR },
.show = queue_requests_show,
@ -478,6 +510,12 @@ static struct queue_sysfs_entry queue_poll_entry = {
.store = queue_poll_store,
};
static struct queue_sysfs_entry queue_wc_entry = {
.attr = {.name = "write_cache", .mode = S_IRUGO | S_IWUSR },
.show = queue_wc_show,
.store = queue_wc_store,
};
static struct attribute *default_attrs[] = {
&queue_requests_entry.attr,
&queue_ra_entry.attr,
@ -503,6 +541,7 @@ static struct attribute *default_attrs[] = {
&queue_iostats_entry.attr,
&queue_random_entry.attr,
&queue_poll_entry.attr,
&queue_wc_entry.attr,
NULL,
};