1 // SPDX-License-Identifier: GPL-2.0 2 3 use core::ops::Deref; 4 5 use kernel::{ 6 alloc::KVec, 7 prelude::*, // 8 }; 9 10 /// A buffer abstraction for discontiguous byte slices. 11 /// 12 /// This allows you to treat multiple non-contiguous `&mut [u8]` slices 13 /// of the same length as a single stream-like read/write buffer. 14 /// 15 /// # Examples 16 /// 17 /// ``` 18 // let mut buf1 = [0u8; 5]; 19 /// let mut buf2 = [0u8; 5]; 20 /// let mut sbuffer = SBufferIter::new_writer([&mut buf1[..], &mut buf2[..]]); 21 /// 22 /// let data = b"hi world!"; 23 /// sbuffer.write_all(data)?; 24 /// drop(sbuffer); 25 /// 26 /// assert_eq!(buf1, *b"hi wo"); 27 /// assert_eq!(buf2, *b"rld!\0"); 28 /// 29 /// # Ok::<(), Error>(()) 30 /// ``` 31 pub(crate) struct SBufferIter<I: Iterator> { 32 // [`Some`] if we are not at the end of the data yet. 33 cur_slice: Option<I::Item>, 34 // All the slices remaining after `cur_slice`. 35 slices: I, 36 } 37 38 impl<'a, I> SBufferIter<I> 39 where 40 I: Iterator, 41 { 42 /// Creates a reader buffer for a discontiguous set of byte slices. 43 /// 44 /// # Examples 45 /// 46 /// ``` 47 /// let buf1: [u8; 5] = [0, 1, 2, 3, 4]; 48 /// let buf2: [u8; 5] = [5, 6, 7, 8, 9]; 49 /// let sbuffer = SBufferIter::new_reader([&buf1[..], &buf2[..]]); 50 /// let sum: u8 = sbuffer.sum(); 51 /// assert_eq!(sum, 45); 52 /// ``` 53 pub(crate) fn new_reader(slices: impl IntoIterator<IntoIter = I>) -> Self 54 where 55 I: Iterator<Item = &'a [u8]>, 56 { 57 Self::new(slices) 58 } 59 60 /// Creates a writeable buffer for a discontiguous set of byte slices. 61 /// 62 /// # Examples 63 /// 64 /// ``` 65 /// let mut buf1 = [0u8; 5]; 66 /// let mut buf2 = [0u8; 5]; 67 /// let mut sbuffer = SBufferIter::new_writer([&mut buf1[..], &mut buf2[..]]); 68 /// sbuffer.write_all(&[0u8, 1, 2, 3, 4, 5, 6, 7, 8, 9][..])?; 69 /// drop(sbuffer); 70 /// assert_eq!(buf1, [0, 1, 2, 3, 4]); 71 /// assert_eq!(buf2, [5, 6, 7, 8, 9]); 72 /// 73 /// ``` 74 pub(crate) fn new_writer(slices: impl IntoIterator<IntoIter = I>) -> Self 75 where 76 I: Iterator<Item = &'a mut [u8]>, 77 { 78 Self::new(slices) 79 } 80 81 fn new(slices: impl IntoIterator<IntoIter = I>) -> Self 82 where 83 I::Item: Deref<Target = [u8]>, 84 { 85 let mut slices = slices.into_iter(); 86 87 Self { 88 // Skip empty slices. 89 cur_slice: slices.find(|s| !s.deref().is_empty()), 90 slices, 91 } 92 } 93 94 /// Returns a slice of at most `len` bytes, or [`None`] if we are at the end of the data. 95 /// 96 /// If a slice shorter than `len` bytes has been returned, the caller can call this method 97 /// again until it returns [`None`] to try and obtain the remainder of the data. 98 /// 99 /// The closure `f` should split the slice received in it's first parameter 100 /// at the position given in the second parameter. 101 fn get_slice_internal( 102 &mut self, 103 len: usize, 104 mut f: impl FnMut(I::Item, usize) -> (I::Item, I::Item), 105 ) -> Option<I::Item> 106 where 107 I::Item: Deref<Target = [u8]>, 108 { 109 match self.cur_slice.take() { 110 None => None, 111 Some(cur_slice) => { 112 if len >= cur_slice.len() { 113 // Caller requested more data than is in the current slice, return it entirely 114 // and prepare the following slice for being used. Skip empty slices to avoid 115 // trouble. 116 self.cur_slice = self.slices.find(|s| !s.is_empty()); 117 118 Some(cur_slice) 119 } else { 120 // The current slice can satisfy the request, split it and return a slice of 121 // the requested size. 122 let (ret, next) = f(cur_slice, len); 123 self.cur_slice = Some(next); 124 125 Some(ret) 126 } 127 } 128 } 129 } 130 131 /// Returns whether this buffer still has data available. 132 pub(crate) fn is_empty(&self) -> bool { 133 self.cur_slice.is_none() 134 } 135 } 136 137 /// Provides a way to get non-mutable slices of data to read from. 138 impl<'a, I> SBufferIter<I> 139 where 140 I: Iterator<Item = &'a [u8]>, 141 { 142 /// Returns a slice of at most `len` bytes, or [`None`] if we are at the end of the data. 143 /// 144 /// If a slice shorter than `len` bytes has been returned, the caller can call this method 145 /// again until it returns [`None`] to try and obtain the remainder of the data. 146 fn get_slice(&mut self, len: usize) -> Option<&'a [u8]> { 147 self.get_slice_internal(len, |s, pos| s.split_at(pos)) 148 } 149 150 /// Ideally we would implement `Read`, but it is not available in `core`. 151 /// So mimic `std::io::Read::read_exact`. 152 #[expect(unused)] 153 pub(crate) fn read_exact(&mut self, mut dst: &mut [u8]) -> Result { 154 while !dst.is_empty() { 155 match self.get_slice(dst.len()) { 156 None => return Err(EINVAL), 157 Some(src) => { 158 let dst_slice; 159 (dst_slice, dst) = dst.split_at_mut(src.len()); 160 dst_slice.copy_from_slice(src); 161 } 162 } 163 } 164 165 Ok(()) 166 } 167 168 /// Read all the remaining data into a [`KVec`]. 169 /// 170 /// `self` will be empty after this operation. 171 #[expect(unused)] 172 pub(crate) fn flush_into_kvec(&mut self, flags: kernel::alloc::Flags) -> Result<KVec<u8>> { 173 let mut buf = KVec::<u8>::new(); 174 175 if let Some(slice) = core::mem::take(&mut self.cur_slice) { 176 buf.extend_from_slice(slice, flags)?; 177 } 178 for slice in &mut self.slices { 179 buf.extend_from_slice(slice, flags)?; 180 } 181 182 Ok(buf) 183 } 184 } 185 186 /// Provides a way to get mutable slices of data to write into. 187 impl<'a, I> SBufferIter<I> 188 where 189 I: Iterator<Item = &'a mut [u8]>, 190 { 191 /// Returns a mutable slice of at most `len` bytes, or [`None`] if we are at the end of the 192 /// data. 193 /// 194 /// If a slice shorter than `len` bytes has been returned, the caller can call this method 195 /// again until it returns `None` to try and obtain the remainder of the data. 196 fn get_slice_mut(&mut self, len: usize) -> Option<&'a mut [u8]> { 197 self.get_slice_internal(len, |s, pos| s.split_at_mut(pos)) 198 } 199 200 /// Ideally we would implement [`Write`], but it is not available in `core`. 201 /// So mimic `std::io::Write::write_all`. 202 pub(crate) fn write_all(&mut self, mut src: &[u8]) -> Result { 203 while !src.is_empty() { 204 match self.get_slice_mut(src.len()) { 205 None => return Err(ETOOSMALL), 206 Some(dst) => { 207 let src_slice; 208 (src_slice, src) = src.split_at(dst.len()); 209 dst.copy_from_slice(src_slice); 210 } 211 } 212 } 213 214 Ok(()) 215 } 216 } 217 218 impl<'a, I> Iterator for SBufferIter<I> 219 where 220 I: Iterator<Item = &'a [u8]>, 221 { 222 type Item = u8; 223 224 fn next(&mut self) -> Option<Self::Item> { 225 // Returned slices are guaranteed to not be empty so we can safely index the first entry. 226 self.get_slice(1).map(|s| s[0]) 227 } 228 } 229