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Fscache/CacheFiles used to serve as a local cache for a remote networking fs. A new on-demand read mode will be introduced for CacheFiles, which can boost the scenario where on-demand read semantics are needed, e.g. container image distribution. The essential difference between these two modes is seen when a cache miss occurs: In the original mode, the netfs will fetch the data from the remote server and then write it to the cache file; in on-demand read mode, fetching the data and writing it into the cache is delegated to a user daemon. As the first step, notify the user daemon when looking up cookie. In this case, an anonymous fd is sent to the user daemon, through which the user daemon can write the fetched data to the cache file. Since the user daemon may move the anonymous fd around, e.g. through dup(), an object ID uniquely identifying the cache file is also attached. Also add one advisory flag (FSCACHE_ADV_WANT_CACHE_SIZE) suggesting that the cache file size shall be retrieved at runtime. This helps the scenario where one cache file contains multiple netfs files, e.g. for the purpose of deduplication. In this case, netfs itself has no idea the size of the cache file, whilst the user daemon should give the hint on it. Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com> Link: https://lore.kernel.org/r/20220509074028.74954-3-jefflexu@linux.alibaba.com Acked-by: David Howells <dhowells@redhat.com> Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
40 lines
1.3 KiB
Text
40 lines
1.3 KiB
Text
# SPDX-License-Identifier: GPL-2.0-only
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config CACHEFILES
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tristate "Filesystem caching on files"
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depends on FSCACHE && BLOCK
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help
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This permits use of a mounted filesystem as a cache for other
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filesystems - primarily networking filesystems - thus allowing fast
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local disk to enhance the speed of slower devices.
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See Documentation/filesystems/caching/cachefiles.rst for more
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information.
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config CACHEFILES_DEBUG
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bool "Debug CacheFiles"
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depends on CACHEFILES
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help
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This permits debugging to be dynamically enabled in the filesystem
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caching on files module. If this is set, the debugging output may be
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enabled by setting bits in /sys/modules/cachefiles/parameter/debug or
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by including a debugging specifier in /etc/cachefilesd.conf.
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config CACHEFILES_ERROR_INJECTION
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bool "Provide error injection for cachefiles"
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depends on CACHEFILES && SYSCTL
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help
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This permits error injection to be enabled in cachefiles whilst a
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cache is in service.
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config CACHEFILES_ONDEMAND
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bool "Support for on-demand read"
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depends on CACHEFILES
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default n
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help
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This permits userspace to enable the cachefiles on-demand read mode.
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In this mode, when a cache miss occurs, responsibility for fetching
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the data lies with the cachefiles backend instead of with the netfs
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and is delegated to userspace.
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If unsure, say N.
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