1.. SPDX-License-Identifier: GPL-2.0 2 3======================= 4Zoned Loop Block Device 5======================= 6 7.. Contents: 8 9 1) Overview 10 2) Creating a Zoned Device 11 3) Deleting a Zoned Device 12 4) Example 13 14 151) Overview 16----------- 17 18The zoned loop block device driver (zloop) allows a user to create a zoned block 19device using one regular file per zone as backing storage. This driver does not 20directly control any hardware and uses read, write and truncate operations to 21regular files of a file system to emulate a zoned block device. 22 23Using zloop, zoned block devices with a configurable capacity, zone size and 24number of conventional zones can be created. The storage for each zone of the 25device is implemented using a regular file with a maximum size equal to the zone 26size. The size of a file backing a conventional zone is always equal to the zone 27size. The size of a file backing a sequential zone indicates the amount of data 28sequentially written to the file, that is, the size of the file directly 29indicates the position of the write pointer of the zone. 30 31When resetting a sequential zone, its backing file size is truncated to zero. 32Conversely, for a zone finish operation, the backing file is truncated to the 33zone size. With this, the maximum capacity of a zloop zoned block device created 34can be larger configured to be larger than the storage space available on the 35backing file system. Of course, for such configuration, writing more data than 36the storage space available on the backing file system will result in write 37errors. 38 39The zoned loop block device driver implements a complete zone transition state 40machine. That is, zones can be empty, implicitly opened, explicitly opened, 41closed or full. The current implementation does not support any limits on the 42maximum number of open and active zones. 43 44No user tools are necessary to create and delete zloop devices. 45 462) Creating a Zoned Device 47-------------------------- 48 49Once the zloop module is loaded (or if zloop is compiled in the kernel), the 50character device file /dev/zloop-control can be used to add a zloop device. 51This is done by writing an "add" command directly to the /dev/zloop-control 52device:: 53 54 $ modprobe zloop 55 $ ls -l /dev/zloop* 56 crw-------. 1 root root 10, 123 Jan 6 19:18 /dev/zloop-control 57 58 $ mkdir -p <base directory/<device ID> 59 $ echo "add [options]" > /dev/zloop-control 60 61The options available for the add command can be listed by reading the 62/dev/zloop-control device:: 63 64 $ cat /dev/zloop-control 65 add id=%d,capacity_mb=%u,zone_size_mb=%u,zone_capacity_mb=%u,conv_zones=%u,max_open_zones=%u,base_dir=%s,nr_queues=%u,queue_depth=%u,buffered_io,zone_append=%u,ordered_zone_append,discard_write_cache 66 remove id=%d 67 68In more details, the options that can be used with the "add" command are as 69follows. 70 71=================== ========================================================= 72id Device number (the X in /dev/zloopX). 73 Default: automatically assigned. 74capacity_mb Device total capacity in MiB. This is always rounded up 75 to the nearest higher multiple of the zone size. 76 Default: 16384 MiB (16 GiB). 77zone_size_mb Device zone size in MiB. Default: 256 MiB. 78zone_capacity_mb Device zone capacity (must always be equal to or lower 79 than the zone size. Default: zone size. 80conv_zones Total number of conventioanl zones starting from 81 sector 0 82 Default: 8 83max_open_zones Maximum number of open sequential write required zones 84 (0 for no limit). 85 Default: 0 86base_dir Path to the base directory where to create the directory 87 containing the zone files of the device. 88 Default=/var/local/zloop. 89 The device directory containing the zone files is always 90 named with the device ID. E.g. the default zone file 91 directory for /dev/zloop0 is /var/local/zloop/0. 92nr_queues Number of I/O queues of the zoned block device. This 93 value is always capped by the number of online CPUs 94 Default: 1 95queue_depth Maximum I/O queue depth per I/O queue. 96 Default: 64 97buffered_io Do buffered IOs instead of direct IOs (default: false) 98zone_append Enable or disable a zloop device native zone append 99 support. 100 Default: 1 (enabled). 101 If native zone append support is disabled, the block layer 102 will emulate this operation using regular write 103 operations. 104ordered_zone_append Enable zloop mitigation of zone append reordering. 105 Default: disabled. 106 This is useful for testing file systems file data mapping 107 (extents), as when enabled, this can significantly reduce 108 the number of data extents needed to for a file data 109 mapping. 110discard_write_cache Discard all data that was not explicitly persisted using a 111 flush operation when the device is removed by truncating 112 each zone file to the size recorded during the last flush 113 operation. This simulates power fail events where 114 uncommitted data is lost. 115=================== ========================================================= 116 1173) Deleting a Zoned Device 118-------------------------- 119 120Deleting an unused zoned loop block device is done by issuing the "remove" 121command to /dev/zloop-control, specifying the ID of the device to remove:: 122 123 $ echo "remove id=X" > /dev/zloop-control 124 125The remove command does not have any option. 126 127A zoned device that was removed can be re-added again without any change to the 128state of the device zones: the device zones are restored to their last state 129before the device was removed. Adding again a zoned device after it was removed 130must always be done using the same configuration as when the device was first 131added. If a zone configuration change is detected, an error will be returned and 132the zoned device will not be created. 133 134To fully delete a zoned device, after executing the remove operation, the device 135base directory containing the backing files of the device zones must be deleted. 136 1374) Example 138---------- 139 140The following sequence of commands creates a 2GB zoned device with zones of 64 141MB and a zone capacity of 63 MB:: 142 143 $ modprobe zloop 144 $ mkdir -p /var/local/zloop/0 145 $ echo "add capacity_mb=2048,zone_size_mb=64,zone_capacity_mb=63" > /dev/zloop-control 146 147For the device created (/dev/zloop0), the zone backing files are all created 148under the default base directory (/var/local/zloop):: 149 150 $ ls -l /var/local/zloop/0 151 total 0 152 -rw-------. 1 root root 67108864 Jan 6 22:23 cnv-000000 153 -rw-------. 1 root root 67108864 Jan 6 22:23 cnv-000001 154 -rw-------. 1 root root 67108864 Jan 6 22:23 cnv-000002 155 -rw-------. 1 root root 67108864 Jan 6 22:23 cnv-000003 156 -rw-------. 1 root root 67108864 Jan 6 22:23 cnv-000004 157 -rw-------. 1 root root 67108864 Jan 6 22:23 cnv-000005 158 -rw-------. 1 root root 67108864 Jan 6 22:23 cnv-000006 159 -rw-------. 1 root root 67108864 Jan 6 22:23 cnv-000007 160 -rw-------. 1 root root 0 Jan 6 22:23 seq-000008 161 -rw-------. 1 root root 0 Jan 6 22:23 seq-000009 162 ... 163 164The zoned device created (/dev/zloop0) can then be used normally:: 165 166 $ lsblk -z 167 NAME ZONED ZONE-SZ ZONE-NR ZONE-AMAX ZONE-OMAX ZONE-APP ZONE-WGRAN 168 zloop0 host-managed 64M 32 0 0 1M 4K 169 $ blkzone report /dev/zloop0 170 start: 0x000000000, len 0x020000, cap 0x020000, wptr 0x000000 reset:0 non-seq:0, zcond: 0(nw) [type: 1(CONVENTIONAL)] 171 start: 0x000020000, len 0x020000, cap 0x020000, wptr 0x000000 reset:0 non-seq:0, zcond: 0(nw) [type: 1(CONVENTIONAL)] 172 start: 0x000040000, len 0x020000, cap 0x020000, wptr 0x000000 reset:0 non-seq:0, zcond: 0(nw) [type: 1(CONVENTIONAL)] 173 start: 0x000060000, len 0x020000, cap 0x020000, wptr 0x000000 reset:0 non-seq:0, zcond: 0(nw) [type: 1(CONVENTIONAL)] 174 start: 0x000080000, len 0x020000, cap 0x020000, wptr 0x000000 reset:0 non-seq:0, zcond: 0(nw) [type: 1(CONVENTIONAL)] 175 start: 0x0000a0000, len 0x020000, cap 0x020000, wptr 0x000000 reset:0 non-seq:0, zcond: 0(nw) [type: 1(CONVENTIONAL)] 176 start: 0x0000c0000, len 0x020000, cap 0x020000, wptr 0x000000 reset:0 non-seq:0, zcond: 0(nw) [type: 1(CONVENTIONAL)] 177 start: 0x0000e0000, len 0x020000, cap 0x020000, wptr 0x000000 reset:0 non-seq:0, zcond: 0(nw) [type: 1(CONVENTIONAL)] 178 start: 0x000100000, len 0x020000, cap 0x01f800, wptr 0x000000 reset:0 non-seq:0, zcond: 1(em) [type: 2(SEQ_WRITE_REQUIRED)] 179 start: 0x000120000, len 0x020000, cap 0x01f800, wptr 0x000000 reset:0 non-seq:0, zcond: 1(em) [type: 2(SEQ_WRITE_REQUIRED)] 180 ... 181 182Deleting this device is done using the command:: 183 184 $ echo "remove id=0" > /dev/zloop-control 185 186The removed device can be re-added again using the same "add" command as when 187the device was first created. To fully delete a zoned device, its backing files 188should also be deleted after executing the remove command:: 189 190 $ rm -r /var/local/zloop/0 191