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,base_dir=%s,nr_queues=%u,queue_depth=%u,buffered_io 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 to 75 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 than 79 the zone size. Default: zone size. 80conv_zones Total number of conventioanl zones starting from sector 0. 81 Default: 8. 82base_dir Path to the base directoy where to create the directory 83 containing the zone files of the device. 84 Default=/var/local/zloop. 85 The device directory containing the zone files is always 86 named with the device ID. E.g. the default zone file 87 directory for /dev/zloop0 is /var/local/zloop/0. 88nr_queues Number of I/O queues of the zoned block device. This value is 89 always capped by the number of online CPUs 90 Default: 1 91queue_depth Maximum I/O queue depth per I/O queue. 92 Default: 64 93buffered_io Do buffered IOs instead of direct IOs (default: false) 94================ =========================================================== 95 963) Deleting a Zoned Device 97-------------------------- 98 99Deleting an unused zoned loop block device is done by issuing the "remove" 100command to /dev/zloop-control, specifying the ID of the device to remove:: 101 102 $ echo "remove id=X" > /dev/zloop-control 103 104The remove command does not have any option. 105 106A zoned device that was removed can be re-added again without any change to the 107state of the device zones: the device zones are restored to their last state 108before the device was removed. Adding again a zoned device after it was removed 109must always be done using the same configuration as when the device was first 110added. If a zone configuration change is detected, an error will be returned and 111the zoned device will not be created. 112 113To fully delete a zoned device, after executing the remove operation, the device 114base directory containing the backing files of the device zones must be deleted. 115 1164) Example 117---------- 118 119The following sequence of commands creates a 2GB zoned device with zones of 64 120MB and a zone capacity of 63 MB:: 121 122 $ modprobe zloop 123 $ mkdir -p /var/local/zloop/0 124 $ echo "add capacity_mb=2048,zone_size_mb=64,zone_capacity=63MB" > /dev/zloop-control 125 126For the device created (/dev/zloop0), the zone backing files are all created 127under the default base directory (/var/local/zloop):: 128 129 $ ls -l /var/local/zloop/0 130 total 0 131 -rw-------. 1 root root 67108864 Jan 6 22:23 cnv-000000 132 -rw-------. 1 root root 67108864 Jan 6 22:23 cnv-000001 133 -rw-------. 1 root root 67108864 Jan 6 22:23 cnv-000002 134 -rw-------. 1 root root 67108864 Jan 6 22:23 cnv-000003 135 -rw-------. 1 root root 67108864 Jan 6 22:23 cnv-000004 136 -rw-------. 1 root root 67108864 Jan 6 22:23 cnv-000005 137 -rw-------. 1 root root 67108864 Jan 6 22:23 cnv-000006 138 -rw-------. 1 root root 67108864 Jan 6 22:23 cnv-000007 139 -rw-------. 1 root root 0 Jan 6 22:23 seq-000008 140 -rw-------. 1 root root 0 Jan 6 22:23 seq-000009 141 ... 142 143The zoned device created (/dev/zloop0) can then be used normally:: 144 145 $ lsblk -z 146 NAME ZONED ZONE-SZ ZONE-NR ZONE-AMAX ZONE-OMAX ZONE-APP ZONE-WGRAN 147 zloop0 host-managed 64M 32 0 0 1M 4K 148 $ blkzone report /dev/zloop0 149 start: 0x000000000, len 0x020000, cap 0x020000, wptr 0x000000 reset:0 non-seq:0, zcond: 0(nw) [type: 1(CONVENTIONAL)] 150 start: 0x000020000, len 0x020000, cap 0x020000, wptr 0x000000 reset:0 non-seq:0, zcond: 0(nw) [type: 1(CONVENTIONAL)] 151 start: 0x000040000, len 0x020000, cap 0x020000, wptr 0x000000 reset:0 non-seq:0, zcond: 0(nw) [type: 1(CONVENTIONAL)] 152 start: 0x000060000, len 0x020000, cap 0x020000, wptr 0x000000 reset:0 non-seq:0, zcond: 0(nw) [type: 1(CONVENTIONAL)] 153 start: 0x000080000, len 0x020000, cap 0x020000, wptr 0x000000 reset:0 non-seq:0, zcond: 0(nw) [type: 1(CONVENTIONAL)] 154 start: 0x0000a0000, len 0x020000, cap 0x020000, wptr 0x000000 reset:0 non-seq:0, zcond: 0(nw) [type: 1(CONVENTIONAL)] 155 start: 0x0000c0000, len 0x020000, cap 0x020000, wptr 0x000000 reset:0 non-seq:0, zcond: 0(nw) [type: 1(CONVENTIONAL)] 156 start: 0x0000e0000, len 0x020000, cap 0x020000, wptr 0x000000 reset:0 non-seq:0, zcond: 0(nw) [type: 1(CONVENTIONAL)] 157 start: 0x000100000, len 0x020000, cap 0x01f800, wptr 0x000000 reset:0 non-seq:0, zcond: 1(em) [type: 2(SEQ_WRITE_REQUIRED)] 158 start: 0x000120000, len 0x020000, cap 0x01f800, wptr 0x000000 reset:0 non-seq:0, zcond: 1(em) [type: 2(SEQ_WRITE_REQUIRED)] 159 ... 160 161Deleting this device is done using the command:: 162 163 $ echo "remove id=0" > /dev/zloop-control 164 165The removed device can be re-added again using the same "add" command as when 166the device was first created. To fully delete a zoned device, its backing files 167should also be deleted after executing the remove command:: 168 169 $ rm -r /var/local/zloop/0 170