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3448914e8c
This allows userspace to completely setup a loop device with a single
ioctl, removing the in-between state where the device can be partially
configured - eg the loop device has a backing file associated with it,
but is reading from the wrong offset.
Besides removing the intermediate state, another big benefit of this
ioctl is that LOOP_SET_STATUS can be slow; the main reason for this
slowness is that LOOP_SET_STATUS(64) calls blk_mq_freeze_queue() to
freeze the associated queue; this requires waiting for RCU
synchronization, which I've measured can take about 15-20ms on this
device on average.
In addition to doing what LOOP_SET_STATUS can do, LOOP_CONFIGURE can
also be used to:
- Set the correct block size immediately by setting
loop_config.block_size (avoids LOOP_SET_BLOCK_SIZE)
- Explicitly request direct I/O mode by setting LO_FLAGS_DIRECT_IO
in loop_config.info.lo_flags (avoids LOOP_SET_DIRECT_IO)
- Explicitly request read-only mode by setting LO_FLAGS_READ_ONLY
in loop_config.info.lo_flags
Here's setting up ~70 regular loop devices with an offset on an x86
Android device, using LOOP_SET_FD and LOOP_SET_STATUS:
vsoc_x86:/system/apex # time for i in `seq 30 100`;
do losetup -r -o 4096 /dev/block/loop$i com.android.adbd.apex; done
0m03.40s real 0m00.02s user 0m00.03s system
Here's configuring ~70 devices in the same way, but using a modified
losetup that uses the new LOOP_CONFIGURE ioctl:
vsoc_x86:/system/apex # time for i in `seq 30 100`;
do losetup -r -o 4096 /dev/block/loop$i com.android.adbd.apex; done
0m01.94s real 0m00.01s user 0m00.01s system
Signed-off-by: Martijn Coenen <maco@android.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
126 lines
3.4 KiB
C
126 lines
3.4 KiB
C
/* SPDX-License-Identifier: GPL-1.0+ WITH Linux-syscall-note */
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/*
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* include/linux/loop.h
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*
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* Written by Theodore Ts'o, 3/29/93.
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*
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* Copyright 1993 by Theodore Ts'o. Redistribution of this file is
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* permitted under the GNU General Public License.
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*/
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#ifndef _UAPI_LINUX_LOOP_H
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#define _UAPI_LINUX_LOOP_H
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#define LO_NAME_SIZE 64
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#define LO_KEY_SIZE 32
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/*
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* Loop flags
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*/
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enum {
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LO_FLAGS_READ_ONLY = 1,
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LO_FLAGS_AUTOCLEAR = 4,
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LO_FLAGS_PARTSCAN = 8,
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LO_FLAGS_DIRECT_IO = 16,
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};
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/* LO_FLAGS that can be set using LOOP_SET_STATUS(64) */
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#define LOOP_SET_STATUS_SETTABLE_FLAGS (LO_FLAGS_AUTOCLEAR | LO_FLAGS_PARTSCAN)
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/* LO_FLAGS that can be cleared using LOOP_SET_STATUS(64) */
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#define LOOP_SET_STATUS_CLEARABLE_FLAGS (LO_FLAGS_AUTOCLEAR)
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/* LO_FLAGS that can be set using LOOP_CONFIGURE */
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#define LOOP_CONFIGURE_SETTABLE_FLAGS (LO_FLAGS_READ_ONLY | LO_FLAGS_AUTOCLEAR \
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| LO_FLAGS_PARTSCAN | LO_FLAGS_DIRECT_IO)
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#include <asm/posix_types.h> /* for __kernel_old_dev_t */
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#include <linux/types.h> /* for __u64 */
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/* Backwards compatibility version */
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struct loop_info {
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int lo_number; /* ioctl r/o */
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__kernel_old_dev_t lo_device; /* ioctl r/o */
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unsigned long lo_inode; /* ioctl r/o */
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__kernel_old_dev_t lo_rdevice; /* ioctl r/o */
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int lo_offset;
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int lo_encrypt_type;
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int lo_encrypt_key_size; /* ioctl w/o */
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int lo_flags;
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char lo_name[LO_NAME_SIZE];
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unsigned char lo_encrypt_key[LO_KEY_SIZE]; /* ioctl w/o */
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unsigned long lo_init[2];
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char reserved[4];
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};
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struct loop_info64 {
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__u64 lo_device; /* ioctl r/o */
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__u64 lo_inode; /* ioctl r/o */
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__u64 lo_rdevice; /* ioctl r/o */
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__u64 lo_offset;
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__u64 lo_sizelimit;/* bytes, 0 == max available */
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__u32 lo_number; /* ioctl r/o */
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__u32 lo_encrypt_type;
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__u32 lo_encrypt_key_size; /* ioctl w/o */
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__u32 lo_flags;
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__u8 lo_file_name[LO_NAME_SIZE];
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__u8 lo_crypt_name[LO_NAME_SIZE];
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__u8 lo_encrypt_key[LO_KEY_SIZE]; /* ioctl w/o */
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__u64 lo_init[2];
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};
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/**
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* struct loop_config - Complete configuration for a loop device.
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* @fd: fd of the file to be used as a backing file for the loop device.
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* @block_size: block size to use; ignored if 0.
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* @info: struct loop_info64 to configure the loop device with.
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*
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* This structure is used with the LOOP_CONFIGURE ioctl, and can be used to
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* atomically setup and configure all loop device parameters at once.
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*/
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struct loop_config {
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__u32 fd;
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__u32 block_size;
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struct loop_info64 info;
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__u64 __reserved[8];
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};
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/*
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* Loop filter types
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*/
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#define LO_CRYPT_NONE 0
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#define LO_CRYPT_XOR 1
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#define LO_CRYPT_DES 2
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#define LO_CRYPT_FISH2 3 /* Twofish encryption */
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#define LO_CRYPT_BLOW 4
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#define LO_CRYPT_CAST128 5
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#define LO_CRYPT_IDEA 6
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#define LO_CRYPT_DUMMY 9
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#define LO_CRYPT_SKIPJACK 10
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#define LO_CRYPT_CRYPTOAPI 18
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#define MAX_LO_CRYPT 20
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/*
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* IOCTL commands --- we will commandeer 0x4C ('L')
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*/
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#define LOOP_SET_FD 0x4C00
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#define LOOP_CLR_FD 0x4C01
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#define LOOP_SET_STATUS 0x4C02
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#define LOOP_GET_STATUS 0x4C03
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#define LOOP_SET_STATUS64 0x4C04
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#define LOOP_GET_STATUS64 0x4C05
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#define LOOP_CHANGE_FD 0x4C06
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#define LOOP_SET_CAPACITY 0x4C07
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#define LOOP_SET_DIRECT_IO 0x4C08
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#define LOOP_SET_BLOCK_SIZE 0x4C09
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#define LOOP_CONFIGURE 0x4C0A
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/* /dev/loop-control interface */
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#define LOOP_CTL_ADD 0x4C80
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#define LOOP_CTL_REMOVE 0x4C81
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#define LOOP_CTL_GET_FREE 0x4C82
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#endif /* _UAPI_LINUX_LOOP_H */
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