b221fc130c
The read request might meet error when searching the btree, but the error was not handled in cache_lookup(), and this kind of metadata failure will not go into cached_dev_read_error(), finally, the upper layer will receive bi_status=0. In this patch we judge the metadata error by the return value of bch_btree_map_keys(), there are two potential paths give rise to the error: 1. Because the btree is not totally cached in memery, we maybe get error when read btree node from cache device (see bch_btree_node_get()), the likely errno is -EIO, -ENOMEM 2. When read miss happens, bch_btree_insert_check_key() will be called to insert a "replace_key" to btree(see cached_dev_cache_miss(), just for doing preparatory work before insert the missed data to cache device), a failure can also happen in this situation, the likely errno is -ENOMEM bch_btree_map_keys() will return MAP_DONE in normal scenario, but we will get either -EIO or -ENOMEM in above two cases. if this happened, we should NOT recover data from backing device (when cache device is dirty) because we don't know whether bkeys the read request covered are all clean. And after that happened, s->iop.status is still its initially value(0) before we submit s->bio.bio, we set it to BLK_STS_IOERR, so it can go into cached_dev_read_error(), and finally it can be passed to upper layer, or recovered by reread from backing device. [edit by mlyle: patch formatting, word-wrap, comment spelling, commit log format] Signed-off-by: Hua Rui <huarui.dev@gmail.com> Reviewed-by: Michael Lyle <mlyle@lyle.org> Signed-off-by: Michael Lyle <mlyle@lyle.org> Signed-off-by: Jens Axboe <axboe@kernel.dk>
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Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.
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