Create a new `MmapGuard`. Memory map the provided open File.
(path: &str)
| 35 | /// |
| 36 | /// Memory map the provided open File. |
| 37 | fn new(path: &str) -> Result<Self, ShmError> { |
| 38 | let mut file = match File::open(path) { |
| 39 | Ok(f) => f, |
| 40 | Err(e) => { |
| 41 | error!(error = ?e, "Failed to open VMClock SHM segment."); |
| 42 | return Err(ShmError::SegmentNotInitialized(format!( |
| 43 | "Failed to open SHM segment at {path}" |
| 44 | ))); |
| 45 | } |
| 46 | }; |
| 47 | |
| 48 | let mut buffer = vec![]; |
| 49 | |
| 50 | let Ok(bytes_read) = file.read_to_end(&mut buffer) else { |
| 51 | return syserror!(String::from("Failed to read SHM segment")); |
| 52 | }; |
| 53 | |
| 54 | if bytes_read == 0_usize { |
| 55 | let msg = String::from("Read zero bytes."); |
| 56 | error!(msg); |
| 57 | return Err(ShmError::SegmentNotInitialized(msg)); |
| 58 | } else if bytes_read < size_of::<VMClockShmHeader>() { |
| 59 | let msg = format!( |
| 60 | "Number of bytes read ({:?}) is less than the size of VMClockShmHeader ({:?}).", |
| 61 | bytes_read, |
| 62 | size_of::<VMClockShmHeader>() |
| 63 | ); |
| 64 | error!(msg); |
| 65 | return Err(ShmError::SegmentMalformed(msg)); |
| 66 | } |
| 67 | |
| 68 | debug!("Reading the VMClockShmHeader."); |
| 69 | |
| 70 | // Read the header so we know how much to map in memory. |
| 71 | let header = VMClockShmHeader::read(&buffer)?; |
| 72 | |
| 73 | // This consumes the segsize, but we only needed the header for validation and extracting |
| 74 | // the segment size. So the move is fine here. |
| 75 | let segsize = header.size.into_inner() as usize; |
| 76 | |
| 77 | debug!("Read a segment size of: {:?}", segsize); |
| 78 | |
| 79 | // SAFETY: We're calling into a C function, but this particular call is always safe. |
| 80 | let segment: *mut c_void = unsafe { |
| 81 | libc::mmap( |
| 82 | ptr::null_mut(), |
| 83 | segsize, |
| 84 | libc::PROT_READ, |
| 85 | libc::MAP_SHARED, |
| 86 | file.as_raw_fd(), |
| 87 | 0, |
| 88 | ) |
| 89 | }; |
| 90 | |
| 91 | if segment == libc::MAP_FAILED { |
| 92 | return syserror!(String::from("Failed to mmap the SHM segment")); |
| 93 | } |
| 94 |