Document the implementation of error handlers into sysfs.
Changelog:
V2:
- Add a description of the precedence order of each option, focusing on
the behavior of "fail_at_unmount" which was not well explained in V1
Signed-off-by: Carlos Maiolino <cmaiolino@xxxxxxxxxx>
---
Documentation/filesystems/xfs.txt | 94 +++++++++++++++++++++++++++++++++++++++
1 file changed, 94 insertions(+)
diff --git a/Documentation/filesystems/xfs.txt b/Documentation/filesystems/xfs.txt
index 8146e9f..d483e0b 100644
--- a/Documentation/filesystems/xfs.txt
+++ b/Documentation/filesystems/xfs.txt
@@ -348,3 +348,97 @@ Removed Sysctls
---- -------
fs.xfs.xfsbufd_centisec v4.0
fs.xfs.age_buffer_centisecs v4.0
+
+Error handling
+==============
+
+XFS can act differently according with the type of error found
+during its operation. The implementation introduces the following
+concepts to the error handler:
+
+ -failure speed:
+ Defines how fast XFS should shutdown in case of a specific
+ error is found during the filesystem operation. It can
+ shutdown immediately, after a defined number of tries, or
+ simply try forever, which was the old behavior and is now
+ set as default behavior, except during unmount time, where
+ in case of a error is found while unmounting, the filesystem
+ will shutdown.
+
+ -error classes:
+ Specifies the subsystem/location where the error handlers
+ configure the behavior for, such as metadata or memory allocation.
+
+ -error handlers:
+ Defines the behavior for a specific error.
+
+The filesystem behavior during an error can be set via sysfs files, where, the
+errors are organized with the following structure:
+
+ /sys/fs/xfs/<dev>/error/<class>/<error>/
+
+Each directory contains:
+
+ /sys/fs/xfs/<dev>/error/
+
+ fail_at_unmount (Min: 0 Default: 1 Max: 1)
+ Defines the global error behavior during unmount time. If set to
+ "1", XFS will shutdown in case of any error is found, otherwise,
+ if set to "0", the filesystem will indefinitely retry to cleanly
+ unmount the filesystem.
+
+ <class> subdirectories
+ Contains specific error handlers configuration
+ (Ex: /sys/fs/xfs/<dev>/error/metadata).
+
+ /sys/fs/xfs/<dev>/error/<class>/
+
+ The contents of this directory are <class> specific, since each <class>
+ might need to handle different types of errors. All <error> directory
+ though, contains the "default" directory, which is a global configuration
+ for errors not available for independent configuration.
+
+ /sys/fs/xfs/<dev>/error/<class>/<error>
+
+ Contains the failure speed configuration files for each specific error,
+ including the "default" behavior, which contains the same configuration
+ options as the specific errors.
+
+ The available configurations for each error type are:
+
+ max_retries (Min: -1 Default: -1 Max: INTMAX)
+ Define how many tries the filesystem is allowed to retry its
+ operations during the specific error, before shutdown the
+ filesystem. Setting this file to "-1", will set XFS to retry
+ forever in the specific error, setting it to "0", will make
+ XFS to fail immediately after the specific error is found,
+ while setting it to a "N" value, where N is greater than 0,
+ will make XFS retry "N" times before shutdown.
+
+ retry_timeout_seconds (Min: 0 Default: 0 Max: INTMAX)
+ Define the amount of time (in seconds) that the filesystem is
+ allowed to retry its operations when the specific error is
+ found. "0" means no wait time.
+
+
+
+ Order of precedence:
+ "max_retries" takes precedence over "retry_timeout_seconds",
+ where, "retry_timeout_seconds" will only be tested if
+ "max_retries" limit was not reached yet or is set to retry
+ forever ("-1"). If "max_retries" limit is reached, the
+ filesystem will shutdown, wether or not "retry_timeout_seconds"
+ has been reached.
+
+ "fail_at_unmount" on the other hand, works independently of the
+ remainder options. It will only be tested during unmount time,
+ but, it will shutdown the filesystem independent of the limits
+ set into "max_retries" or "retry_timeout_seconds".
+ It has been added because sysfs configuration can't be changed
+ after an unmount is triggered, once the sysfs directory from
+ the filesystem being unmounted will be detached from the sysfs
+ tree, so, even if the sysadmin wants to make XFS retry forever
+ for any error during the filesystem operation, the filesystem
+ can still be properly unmounted if any error was detected and
+ "fail_at_unmount" is set. Otherwise, the umount process get
+ stuck forever.
--
2.5.5
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