diff options
Diffstat (limited to 'Documentation/filesystems/zonefs.txt')
-rw-r--r-- | Documentation/filesystems/zonefs.txt | 36 |
1 files changed, 22 insertions, 14 deletions
diff --git a/Documentation/filesystems/zonefs.txt b/Documentation/filesystems/zonefs.txt index 935bf22031ca..78813c34ec47 100644 --- a/Documentation/filesystems/zonefs.txt +++ b/Documentation/filesystems/zonefs.txt @@ -134,7 +134,7 @@ Sequential zone files can only be written sequentially, starting from the file end, that is, write operations can only be append writes. Zonefs makes no attempt at accepting random writes and will fail any write request that has a start offset not corresponding to the end of the file, or to the end of the last -write issued and still in-flight (for asynchrnous I/O operations). +write issued and still in-flight (for asynchronous I/O operations). Since dirty page writeback by the page cache does not guarantee a sequential write pattern, zonefs prevents buffered writes and writeable shared mappings @@ -142,7 +142,7 @@ on sequential files. Only direct I/O writes are accepted for these files. zonefs relies on the sequential delivery of write I/O requests to the device implemented by the block layer elevator. An elevator implementing the sequential write feature for zoned block device (ELEVATOR_F_ZBD_SEQ_WRITE elevator feature) -must be used. This type of elevator (e.g. mq-deadline) is the set by default +must be used. This type of elevator (e.g. mq-deadline) is set by default for zoned block devices on device initialization. There are no restrictions on the type of I/O used for read operations in @@ -196,7 +196,7 @@ additional conditions that result in I/O errors. may still happen in the case of a partial failure of a very large direct I/O operation split into multiple BIOs/requests or asynchronous I/O operations. If one of the write request within the set of sequential write requests - issued to the device fails, all write requests after queued after it will + issued to the device fails, all write requests queued after it will become unaligned and fail. * Delayed write errors: similarly to regular block devices, if the device side @@ -207,7 +207,7 @@ additional conditions that result in I/O errors. causing all data to be dropped after the sector that caused the error. All I/O errors detected by zonefs are notified to the user with an error code -return for the system call that trigered or detected the error. The recovery +return for the system call that triggered or detected the error. The recovery actions taken by zonefs in response to I/O errors depend on the I/O type (read vs write) and on the reason for the error (bad sector, unaligned writes or zone condition change). @@ -222,7 +222,7 @@ condition change). * A zone condition change to read-only or offline also always triggers zonefs I/O error recovery. -Zonefs minimal I/O error recovery may change a file size and a file access +Zonefs minimal I/O error recovery may change a file size and file access permissions. * File size changes: @@ -237,7 +237,7 @@ permissions. A file size may also be reduced to reflect a delayed write error detected on fsync(): in this case, the amount of data effectively written in the zone may be less than originally indicated by the file inode size. After such I/O - error, zonefs always fixes a file inode size to reflect the amount of data + error, zonefs always fixes the file inode size to reflect the amount of data persistently stored in the file zone. * Access permission changes: @@ -258,11 +258,11 @@ conditions. | option | condition | size read write read write | +--------------+-----------+-----------------------------------------+ | | good | fixed yes no yes yes | - | remount-ro | read-only | fixed yes no yes no | + | remount-ro | read-only | as is yes no yes no | | (default) | offline | 0 no no no no | +--------------+-----------+-----------------------------------------+ | | good | fixed yes no yes yes | - | zone-ro | read-only | fixed yes no yes no | + | zone-ro | read-only | as is yes no yes no | | | offline | 0 no no no no | +--------------+-----------+-----------------------------------------+ | | good | 0 no no yes yes | @@ -270,7 +270,7 @@ conditions. | | offline | 0 no no no no | +--------------+-----------+-----------------------------------------+ | | good | fixed yes yes yes yes | - | repair | read-only | fixed yes no yes no | + | repair | read-only | as is yes no yes no | | | offline | 0 no no no no | +--------------+-----------+-----------------------------------------+ @@ -281,11 +281,11 @@ Further notes: permissions to read-only applies to all files. The file system is remounted read-only. * Access permission and file size changes due to the device transitioning zones - to the offline condition are permanent. Remounting or reformating the device + to the offline condition are permanent. Remounting or reformatting the device with mkfs.zonefs (mkzonefs) will not change back offline zone files to a good state. * File access permission changes to read-only due to the device transitioning - zones to the read-only condition are permanent. Remounting or reformating + zones to the read-only condition are permanent. Remounting or reformatting the device will not re-enable file write access. * File access permission changes implied by the remount-ro, zone-ro and zone-offline mount options are temporary for zones in a good condition. @@ -301,14 +301,22 @@ Mount options zonefs define the "errors=<behavior>" mount option to allow the user to specify zonefs behavior in response to I/O errors, inode size inconsistencies or zone -condition chages. The defined behaviors are as follow: +condition changes. The defined behaviors are as follow: * remount-ro (default) * zone-ro * zone-offline * repair -The I/O error actions defined for each behavior is detailed in the previous -section. +The run-time I/O error actions defined for each behavior are detailed in the +previous section. Mount time I/O errors will cause the mount operation to fail. +The handling of read-only zones also differs between mount-time and run-time. +If a read-only zone is found at mount time, the zone is always treated in the +same manner as offline zones, that is, all accesses are disabled and the zone +file size set to 0. This is necessary as the write pointer of read-only zones +is defined as invalib by the ZBC and ZAC standards, making it impossible to +discover the amount of data that has been written to the zone. In the case of a +read-only zone discovered at run-time, as indicated in the previous section. +the size of the zone file is left unchanged from its last updated value. Zonefs User Space Tools ======================= |