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https://github.com/torvalds/linux
27 March 2024, 02:37:15 UTC
Revision db3b5848ea6440968fcdd29b80514d0de044bb7c authored by Kiyoshi Ueda on 17 June 2005, 14:15:10 UTC, committed by Jens Axboe on 17 June 2005, 14:15:10 UTC 
When cfq I/O scheduler is selected, get_request() in __make_request() calls
 
__cfq_get_queue().  __cfq_get_queue() finds an existing queue (struct
cfq_queue) of the current process for the device and returns it.  If it's not
found, __cfq_get_queue() creates and returns a new one if __cfq_get_queue() is
called with __GFP_WAIT flag, or __cfq_get_queue() returns NULL (this means that
get_request() fails) if no __GFP_WAIT flag.

On the other hand, in __make_request(), get_request() is called without
__GFP_WAIT flag at the first time.  Thus, the get_request() fails when there is
no existing queue, typically when it's called for the first I/O request of the
process to the device.

Though it will be followed by get_request_wait() for general case,
__make_request() will just end the I/O with an error (EWOULDBLOCK) when the
request was for read-ahead.

Signed-off-by: Jens Axboe <axboe@suse.de>
Signed-off-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
1 parent c374f12
History
Tip revision: db3b5848ea6440968fcdd29b80514d0de044bb7c authored by Kiyoshi Ueda on 17 June 2005, 14:15:10 UTC
When cfq I/O scheduler is selected, get_request() in __make_request() calls
Tip revision: db3b584
File Mode Size
Kconfig -rw-r--r-- 17.4 KB
Makefile -rw-r--r-- 895 bytes
calibrate.c -rw-r--r-- 1.8 KB
do_mounts.c -rw-r--r-- 9.1 KB
do_mounts.h -rw-r--r-- 1.7 KB
do_mounts_devfs.c -rw-r--r-- 2.8 KB
do_mounts_initrd.c -rw-r--r-- 2.9 KB
do_mounts_md.c -rw-r--r-- 7.6 KB
do_mounts_rd.c -rw-r--r-- 10.0 KB
initramfs.c -rw-r--r-- 9.9 KB
main.c -rw-r--r-- 16.4 KB
version.c -rw-r--r-- 748 bytes
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