Struct QueueLimits 

pub struct QueueLimits {
    pub page: usize,
    pub logical_block: usize,
    pub max_request: usize,
    pub nr_requests: usize,
    pub read_ahead: usize,
    pub nr_hw_queues: usize,
    pub rotational: bool,
}

Limits read from the block queue that holds path.

max_request is max_sectors_kb times 1024, the largest request that queue accepts (https://docs.kernel.org/admin-guide/abi-stable.html#abi-sys-block-disk-queue-max-sectors-kb). nr_requests is how many requests the queue can hold (https://docs.kernel.org/admin-guide/abi-stable.html#abi-sys-block-disk-queue-nr-requests). read_ahead is read_ahead_kb times 1024, the kernel readahead window. A partition is walked to its parent disk, which is the sysfs node that holds queue/. A missing queue file yields the page size, the unit madvise accepts, and a missing nr_requests yields 1. rotational is recorded and does not select the plan.

Fields

page: usize

logical_block: usize

max_request: usize

nr_requests: usize

read_ahead: usize

nr_hw_queues: usize

Hardware queues. blk-mq applies nr_requests to each one.

rotational: bool

queue/rotational is 1 when the queue file says so. The flag is recorded. It does not select the read plan.

Implementations

impl QueueLimits

pub fn page_default(page: usize) -> Self

Page-sized stand-in used when the file has no block queue.

btrfs, tmpfs, overlayfs and NFS have no queue/ directory. The page is the unit madvise accepts, so one request of one page is the stand-in.

pub fn of(path: &Path) -> Result<Self, ParseError>

pub fn worker_span(&self, workers: usize) -> usize

Bytes one worker submits while the others share the same queue.

The queue holds nr_requests requests of max_request bytes. workers share it, so each gets nr_requests / workers requests, or one request when the queue is shorter than the worker count. The span is at least the kernel readahead window, because a shorter hint still pulls that window, and it is aligned down to the page.

Trait Implementations

impl Clone for QueueLimits

fn clone(&self) -> Self

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for QueueLimits

impl Debug for QueueLimits

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.