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Commit 32fab448e5e86694beade415e750363538ea5f49

Authored by Kiyoshi Ueda
Committed by Jens Axboe
1 parent e3335de940
Exists in master and in 7 other branches imx_3.0.35_4.1.0, imx_3.10.17_1.0.1_ga, imx_3.10.53_1.1.0_ga, imx_3.14.28_1.0.0_ga, smarc-imx_3.10.53_1.1.0_ga, smarc-imx_3.14.28_1.0.0_ga, smarc-l5.0.0_1.0.0-ga

block: add request update interface 

This patch adds blk_update_request(), which updates struct request
with completing its data part, but doesn't complete the struct
request itself.
Though it looks like end_that_request_first() of older kernels,
blk_update_request() should be used only by request stacking drivers.

Request-based dm will use it in bio->bi_end_io callback to update
the original request when a data part of a cloned request completes.
Followings are additional background information of why request-based
dm needs this interface.

  - Request stacking drivers can't use blk_end_request() directly from
    the lower driver's completion context (bio->bi_end_io or rq->end_io),
    because some device drivers (e.g. ide) may try to complete
    their request with queue lock held, and it may cause deadlock.
    See below for detailed description of possible deadlock:
    <http://marc.info/?l=linux-kernel&m=120311479108569&w=2>

  - To solve that, request-based dm offloads the completion of
    cloned struct request to softirq context (i.e. using
    blk_complete_request() from rq->end_io).

  - Though it is possible to use the same solution from bio->bi_end_io,
    it will delay the notification of bio completion to the original
    submitter.  Also, it will cause inefficient partial completion,
    because the lower driver can't perform the cloned request anymore
    and request-based dm needs to requeue and redispatch it to
    the lower driver again later.  That's not good.

  - So request-based dm needs blk_update_request() to perform the bio
    completion in the lower driver's completion context, which is more
    efficient.

Signed-off-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

Showing 2 changed files with 50 additions and 9 deletions Side-by-side Diff

... ... @@ -1806,6 +1806,22 @@
1806 1806 }
1807 1807 EXPORT_SYMBOL(end_request);
1808 1808  
  1809 +static int end_that_request_data(struct request *rq, int error,
  1810 + unsigned int nr_bytes, unsigned int bidi_bytes)
  1811 +{
  1812 + if (rq->bio) {
  1813 + if (__end_that_request_first(rq, error, nr_bytes))
  1814 + return 1;
  1815 +
  1816 + /* Bidi request must be completed as a whole */
  1817 + if (blk_bidi_rq(rq) &&
  1818 + __end_that_request_first(rq->next_rq, error, bidi_bytes))
  1819 + return 1;
  1820 + }
  1821 +
  1822 + return 0;
  1823 +}
  1824 +
1809 1825 /**
1810 1826 * blk_end_io - Generic end_io function to complete a request.
1811 1827 * @rq: the request being processed
1812 1828  
... ... @@ -1832,16 +1848,9 @@
1832 1848 struct request_queue *q = rq->q;
1833 1849 unsigned long flags = 0UL;
1834 1850  
1835   - if (rq->bio) {
1836   - if (__end_that_request_first(rq, error, nr_bytes))
1837   - return 1;
  1851 + if (end_that_request_data(rq, error, nr_bytes, bidi_bytes))
  1852 + return 1;
1838 1853  
1839   - /* Bidi request must be completed as a whole */
1840   - if (blk_bidi_rq(rq) &&
1841   - __end_that_request_first(rq->next_rq, error, bidi_bytes))
1842   - return 1;
1843   - }
1844   -
1845 1854 /* Special feature for tricky drivers */
1846 1855 if (drv_callback && drv_callback(rq))
1847 1856 return 1;
... ... @@ -1921,6 +1930,36 @@
1921 1930 return blk_end_io(rq, error, nr_bytes, bidi_bytes, NULL);
1922 1931 }
1923 1932 EXPORT_SYMBOL_GPL(blk_end_bidi_request);
  1933 +
  1934 +/**
  1935 + * blk_update_request - Special helper function for request stacking drivers
  1936 + * @rq: the request being processed
  1937 + * @error: %0 for success, < %0 for error
  1938 + * @nr_bytes: number of bytes to complete @rq
  1939 + *
  1940 + * Description:
  1941 + * Ends I/O on a number of bytes attached to @rq, but doesn't complete
  1942 + * the request structure even if @rq doesn't have leftover.
  1943 + * If @rq has leftover, sets it up for the next range of segments.
  1944 + *
  1945 + * This special helper function is only for request stacking drivers
  1946 + * (e.g. request-based dm) so that they can handle partial completion.
  1947 + * Actual device drivers should use blk_end_request instead.
  1948 + */
  1949 +void blk_update_request(struct request *rq, int error, unsigned int nr_bytes)
  1950 +{
  1951 + if (!end_that_request_data(rq, error, nr_bytes, 0)) {
  1952 + /*
  1953 + * These members are not updated in end_that_request_data()
  1954 + * when all bios are completed.
  1955 + * Update them so that the request stacking driver can find
  1956 + * how many bytes remain in the request later.
  1957 + */
  1958 + rq->nr_sectors = rq->hard_nr_sectors = 0;
  1959 + rq->current_nr_sectors = rq->hard_cur_sectors = 0;
  1960 + }
  1961 +}
  1962 +EXPORT_SYMBOL_GPL(blk_update_request);
1924 1963  
1925 1964 /**
1926 1965 * blk_end_request_callback - Special helper function for tricky drivers
include/linux/blkdev.h
Diff comments   View file @ 32fab44
... ... @@ -791,6 +791,8 @@
791 791 extern void __blk_complete_request(struct request *);
792 792 extern void blk_abort_request(struct request *);
793 793 extern void blk_abort_queue(struct request_queue *);
  794 +extern void blk_update_request(struct request *rq, int error,
  795 + unsigned int nr_bytes);
794 796  
795 797 /*
796 798 * blk_end_request() takes bytes instead of sectors as a complete size.