vmo_blob/
lib.rs

1// Copyright 2023 The Fuchsia Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5use anyhow::{anyhow, Error};
6use fidl_fuchsia_io as fio;
7use log::error;
8use std::sync::{Arc, OnceLock};
9use vfs::directory::entry::{EntryInfo, GetEntryInfo};
10use vfs::file::{File, FileOptions, GetVmo, SyncMode};
11use vfs::immutable_attributes;
12
13/// Mimics the c++ blobfs block size.
14const BLOCK_SIZE: u64 = 8192;
15static VMEX_RESOURCE: OnceLock<zx::Resource> = OnceLock::new();
16
17/// Attempt to initialize the vmex resource. Without a vmex, attempts to get the backing memory
18/// of a blob with executable rights will fail with NOT_SUPPORTED.
19pub fn init_vmex_resource(vmex: zx::Resource) -> Result<(), Error> {
20    VMEX_RESOURCE.set(vmex).map_err(|_| anyhow!(zx::Status::ALREADY_BOUND))
21}
22
23/// `VmoBlob` is a wrapper around the fuchsia.io/File protocol. Represents an immutable blob on
24/// Fxfs. Clients will use this library to read and execute blobs.
25pub struct VmoBlob {
26    vmo: zx::Vmo,
27}
28
29impl VmoBlob {
30    pub fn new(vmo: zx::Vmo) -> Arc<Self> {
31        Arc::new(Self { vmo })
32    }
33}
34
35impl GetVmo for VmoBlob {
36    fn get_vmo(&self) -> &zx::Vmo {
37        &self.vmo
38    }
39}
40
41impl GetEntryInfo for VmoBlob {
42    fn entry_info(&self) -> EntryInfo {
43        EntryInfo::new(fio::INO_UNKNOWN, fio::DirentType::File)
44    }
45}
46
47impl vfs::node::Node for VmoBlob {
48    async fn get_attributes(
49        &self,
50        requested_attributes: fio::NodeAttributesQuery,
51    ) -> Result<fio::NodeAttributes2, zx::Status> {
52        let content_size = self.get_size().await?;
53        Ok(immutable_attributes!(
54            requested_attributes,
55            Immutable {
56                protocols: fio::NodeProtocolKinds::FILE,
57                abilities: fio::Operations::GET_ATTRIBUTES
58                    | fio::Operations::READ_BYTES
59                    | fio::Operations::EXECUTE,
60                content_size: content_size,
61                // TODO(https://fxbug.dev/295550170): Get storage_size from fxblob.
62                storage_size: content_size.div_ceil(BLOCK_SIZE) * BLOCK_SIZE,
63            }
64        ))
65    }
66}
67
68/// Implement VFS trait so blobs can be accessed as files.
69impl File for VmoBlob {
70    fn executable(&self) -> bool {
71        true
72    }
73
74    async fn open_file(&self, _options: &FileOptions) -> Result<(), zx::Status> {
75        Ok(())
76    }
77
78    async fn truncate(&self, _length: u64) -> Result<(), zx::Status> {
79        Err(zx::Status::ACCESS_DENIED)
80    }
81
82    async fn get_size(&self) -> Result<u64, zx::Status> {
83        self.vmo.get_content_size()
84    }
85
86    async fn get_backing_memory(&self, flags: fio::VmoFlags) -> Result<zx::Vmo, zx::Status> {
87        // We do not support exact/duplicate sharing mode.
88        if flags.contains(fio::VmoFlags::SHARED_BUFFER) {
89            error!("get_backing_memory does not support exact sharing mode!");
90            return Err(zx::Status::NOT_SUPPORTED);
91        }
92        // We only support the combination of WRITE when a private COW clone is explicitly
93        // specified. This implicitly restricts any mmap call that attempts to use MAP_SHARED +
94        // PROT_WRITE.
95        if flags.contains(fio::VmoFlags::WRITE) && !flags.contains(fio::VmoFlags::PRIVATE_CLONE) {
96            error!("get_buffer only supports VmoFlags::WRITE with VmoFlags::PRIVATE_CLONE!");
97            return Err(zx::Status::NOT_SUPPORTED);
98        }
99
100        // If the VMO we return is not going to be written to then we can return a REFERENCE instead
101        // of a SNAPSHOT child, which has a more efficient kernel representation.
102        let use_reference = !flags.contains(fio::VmoFlags::WRITE);
103        let child_options = if use_reference {
104            zx::VmoChildOptions::REFERENCE | zx::VmoChildOptions::NO_WRITE
105        } else {
106            zx::VmoChildOptions::SNAPSHOT_AT_LEAST_ON_WRITE
107        };
108        let child_size = if use_reference { 0 } else { self.vmo.get_content_size()? };
109        let mut child_vmo = self.vmo.create_child(child_options, 0, child_size)?;
110
111        if flags.contains(fio::VmoFlags::EXECUTE) {
112            // TODO(https://fxbug.dev/293606235): Filter out other flags.
113            child_vmo = child_vmo
114                .replace_as_executable(VMEX_RESOURCE.get().ok_or(zx::Status::NOT_SUPPORTED)?)?;
115        }
116
117        Ok(child_vmo)
118    }
119
120    async fn update_attributes(
121        &self,
122        _attributes: fio::MutableNodeAttributes,
123    ) -> Result<(), zx::Status> {
124        Err(zx::Status::NOT_SUPPORTED)
125    }
126
127    async fn sync(&self, _mode: SyncMode) -> Result<(), zx::Status> {
128        Ok(())
129    }
130}
vmo_blob/lib.rs

vmo_blob/
lib.rs
