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45f9b32e SR |
1 | use anyhow::Error; |
2 | use std::fs::{File, OpenOptions}; | |
3 | use std::path::Path; | |
4 | use std::os::unix::io::{RawFd, AsRawFd}; | |
5 | ||
6 | const LOOP_CONTROL: &str = "/dev/loop-control"; | |
7 | const LOOP_NAME: &str = "/dev/loop"; | |
8 | ||
9 | /// Implements a subset of loop device ioctls necessary to assign and release | |
10 | /// a single file from a free loopdev. | |
11 | mod loop_ioctl { | |
12 | use nix::{ioctl_none, ioctl_write_int_bad, ioctl_write_ptr_bad}; | |
13 | ||
14 | const LOOP_IOCTL: u16 = 0x4C; // 'L' | |
15 | const LOOP_SET_FD: u16 = 0x00; | |
16 | const LOOP_CLR_FD: u16 = 0x01; | |
17 | const LOOP_SET_STATUS64: u16 = 0x04; | |
18 | ||
19 | const LOOP_CTRL_GET_FREE: u16 = 0x82; | |
20 | ||
21 | ioctl_write_int_bad!(ioctl_set_fd, (LOOP_IOCTL << 8) | LOOP_SET_FD); | |
22 | ioctl_none!(ioctl_clr_fd, LOOP_IOCTL, LOOP_CLR_FD); | |
23 | ioctl_none!(ioctl_ctrl_get_free, LOOP_IOCTL, LOOP_CTRL_GET_FREE); | |
24 | ioctl_write_ptr_bad!(ioctl_set_status64, (LOOP_IOCTL << 8) | LOOP_SET_STATUS64, LoopInfo64); | |
25 | ||
26 | pub const LO_FLAGS_READ_ONLY: u32 = 1; | |
27 | pub const LO_FLAGS_PARTSCAN: u32 = 8; | |
28 | ||
29 | const LO_NAME_SIZE: usize = 64; | |
30 | const LO_KEY_SIZE: usize = 32; | |
31 | ||
32 | #[repr(C)] | |
33 | pub struct LoopInfo64 { | |
34 | pub lo_device: u64, | |
35 | pub lo_inode: u64, | |
36 | pub lo_rdevice: u64, | |
37 | pub lo_offset: u64, | |
38 | pub lo_sizelimit: u64, | |
39 | pub lo_number: u32, | |
40 | pub lo_encrypt_type: u32, | |
41 | pub lo_encrypt_key_size: u32, | |
42 | pub lo_flags: u32, | |
43 | pub lo_file_name: [u8; LO_NAME_SIZE], | |
44 | pub lo_crypt_name: [u8; LO_NAME_SIZE], | |
45 | pub lo_encrypt_key: [u8; LO_KEY_SIZE], | |
46 | pub lo_init: [u64; 2], | |
47 | } | |
48 | } | |
49 | ||
50 | // ioctl helpers create public fns, do not export them outside the module | |
51 | // users should use the wrapper functions below | |
52 | use loop_ioctl::*; | |
53 | ||
54 | /// Use the GET_FREE ioctl to get or add a free loop device, of which the | |
55 | /// /dev/loopN path will be returned. This is inherently racy because of the | |
56 | /// delay between this and calling assign, but since assigning is atomic it | |
57 | /// does not matter much and will simply cause assign to fail. | |
58 | pub fn get_or_create_free_dev() -> Result<String, Error> { | |
59 | let ctrl_file = File::open(LOOP_CONTROL)?; | |
60 | let free_num = unsafe { ioctl_ctrl_get_free(ctrl_file.as_raw_fd())? }; | |
61 | let loop_file_path = format!("{}{}", LOOP_NAME, free_num); | |
62 | Ok(loop_file_path) | |
63 | } | |
64 | ||
65 | fn assign_dev(fd: RawFd, backing_fd: RawFd) -> Result<(), Error> { | |
66 | unsafe { ioctl_set_fd(fd, backing_fd)?; } | |
67 | ||
68 | // set required read-only flag and partscan for convenience | |
69 | let mut info: LoopInfo64 = unsafe { std::mem::zeroed() }; | |
70 | info.lo_flags = LO_FLAGS_READ_ONLY | LO_FLAGS_PARTSCAN; | |
71 | unsafe { ioctl_set_status64(fd, &info)?; } | |
72 | ||
73 | Ok(()) | |
74 | } | |
75 | ||
76 | /// Open the next available /dev/loopN file and assign the given path to | |
77 | /// it as it's backing file in read-only mode. | |
78 | pub fn assign<P: AsRef<Path>>(loop_dev: P, backing: P) -> Result<(), Error> { | |
79 | let loop_file = File::open(loop_dev)?; | |
80 | let backing_file = OpenOptions::new() | |
81 | .read(true) | |
82 | .open(backing)?; | |
83 | assign_dev(loop_file.as_raw_fd(), backing_file.as_raw_fd())?; | |
84 | Ok(()) | |
85 | } | |
86 | ||
87 | /// Unassign any file descriptors currently attached to the given | |
88 | /// /dev/loopN device. | |
89 | pub fn unassign<P: AsRef<Path>>(path: P) -> Result<(), Error> { | |
90 | let loop_file = File::open(path)?; | |
91 | unsafe { ioctl_clr_fd(loop_file.as_raw_fd())?; } | |
92 | Ok(()) | |
93 | } |