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linux-next/include/linux/errseq.h

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Documentation: add some docs for errseq_t ...and fix up a few comments in the code. Signed-off-by: Jeff Layton <jlayton@redhat.com>
2017-07-24 18:22:16 +08:00
/*
* See Documentation/errseq.rst and lib/errseq.c
*/
lib: add errseq_t type and infrastructure for handling it An errseq_t is a way of recording errors in one place, and allowing any number of "subscribers" to tell whether an error has been set again since a previous time. It's implemented as an unsigned 32-bit value that is managed with atomic operations. The low order bits are designated to hold an error code (max size of MAX_ERRNO). The upper bits are used as a counter. The API works with consumers sampling an errseq_t value at a particular point in time. Later, that value can be used to tell whether new errors have been set since that time. Note that there is a 1 in 512k risk of collisions here if new errors are being recorded frequently, since we have so few bits to use as a counter. To mitigate this, one bit is used as a flag to tell whether the value has been sampled since a new value was recorded. That allows us to avoid bumping the counter if no one has sampled it since it was last bumped. Later patches will build on this infrastructure to change how writeback errors are tracked in the kernel. Signed-off-by: Jeff Layton <jlayton@redhat.com> Reviewed-by: NeilBrown <neilb@suse.com> Reviewed-by: Jan Kara <jack@suse.cz>
2017-07-06 19:02:24 +08:00
#ifndef _LINUX_ERRSEQ_H
#define _LINUX_ERRSEQ_H
typedef u32 errseq_t;
errseq: rename __errseq_set to errseq_set Nothing calls this wrapper anymore, so just remove it and rename the old function to get rid of the double underscore prefix. Signed-off-by: Jeff Layton <jlayton@redhat.com>
2017-07-24 18:22:15 +08:00
errseq_t errseq_set(errseq_t *eseq, int err);
lib: add errseq_t type and infrastructure for handling it An errseq_t is a way of recording errors in one place, and allowing any number of "subscribers" to tell whether an error has been set again since a previous time. It's implemented as an unsigned 32-bit value that is managed with atomic operations. The low order bits are designated to hold an error code (max size of MAX_ERRNO). The upper bits are used as a counter. The API works with consumers sampling an errseq_t value at a particular point in time. Later, that value can be used to tell whether new errors have been set since that time. Note that there is a 1 in 512k risk of collisions here if new errors are being recorded frequently, since we have so few bits to use as a counter. To mitigate this, one bit is used as a flag to tell whether the value has been sampled since a new value was recorded. That allows us to avoid bumping the counter if no one has sampled it since it was last bumped. Later patches will build on this infrastructure to change how writeback errors are tracked in the kernel. Signed-off-by: Jeff Layton <jlayton@redhat.com> Reviewed-by: NeilBrown <neilb@suse.com> Reviewed-by: Jan Kara <jack@suse.cz>
2017-07-06 19:02:24 +08:00
errseq_t errseq_sample(errseq_t *eseq);
int errseq_check(errseq_t *eseq, errseq_t since);
int errseq_check_and_advance(errseq_t *eseq, errseq_t *since);
#endif
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