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// Copyright (c) 2023 Nick Piaddo
// SPDX-License-Identifier: Apache-2.0 OR MIT
// From dependency library
// From standard library
use std::mem::MaybeUninit;
use std::num::NonZeroUsize;
// From this library
use crate::core::entries::MountInfoEntry;
use crate::core::errors::MountInfoIterError;
use crate::core::iter::{Direction, GenIterator};
use crate::owning_ref_from_ptr;
use crate::tables::MountInfo;
/// Iterator over [`MountInfo`] entries.
#[derive(Debug)]
pub struct MountInfoIter<'table> {
table: &'table MountInfo,
/// Forward iterator.
fwd_iter: GenIterator,
/// Backward iterator.
bwd_iter: GenIterator,
/// Current item in forward iteration.
fwd_cursor: *mut libmount::libmnt_fs,
/// Current item in backward iteration.
bwd_cursor: *mut libmount::libmnt_fs,
/// Indicator of forward and backward iterators meeting in the middle.
have_iterators_met: bool,
}
impl<'table> MountInfoIter<'table> {
/// Creates a new `MountInfoIter`.
#[allow(dead_code)]
pub(crate) fn new(
table: &'table MountInfo,
) -> Result<MountInfoIter<'table>, MountInfoIterError> {
let fwd_iter = GenIterator::new(Direction::Forward)?;
let bwd_iter = GenIterator::new(Direction::Backward)?;
let fwd_cursor = std::ptr::null_mut();
let bwd_cursor = std::ptr::null_mut();
let have_iterators_met = false;
let iterator = Self {
table,
fwd_iter,
bwd_iter,
fwd_cursor,
bwd_cursor,
have_iterators_met,
};
Ok(iterator)
}
/// Advances the iterator by `n` elements.
///
/// This method will eagerly skip `n` elements. The following call to `next()` will
/// yield the element at index `n+1`.
///
/// `advance_to(n)` will return `Ok(())` if the iterator successfully advances by
/// `n` elements, or a `Err(NonZeroUsize)` with value `k`, if an eror occurs or if
/// it reaches the end of the iterator, where `k` is the remaining number of steps that
/// could not be advanced because the iterator ran out.
///
/// If `self` is empty and `n` is non-zero, then this returns `Err(n)`. Otherwise,
/// `k` is always less than `n`.
pub fn advance_to(&mut self, n: usize) -> Result<(), NonZeroUsize> {
// Reset iterator
self.fwd_iter.reset();
self.bwd_iter.reset();
self.fwd_cursor = std::ptr::null_mut();
self.bwd_cursor = std::ptr::null_mut();
self.have_iterators_met = false;
let mut result;
for i in 0..=n {
let mut entry_ptr = MaybeUninit::<*mut libmount::libmnt_fs>::zeroed();
result = unsafe {
libmount::mnt_table_next_fs(
self.table.inner,
self.fwd_iter.inner,
entry_ptr.as_mut_ptr(),
)
};
match result {
0 => {
let ptr = unsafe { entry_ptr.assume_init() };
// Per the documentation of `DoubleEndedIterator`
// "It is important to note that both back and forth work on the same range, and do not cross: iteration is over when they meet in the middle."
if self.have_iterators_met
|| (self.fwd_cursor != self.bwd_cursor && ptr == self.bwd_cursor)
{
log::debug!(
"MountInfoIter::advance_to forward and backward iterators have met in the middle"
);
self.have_iterators_met = true;
return Err(unsafe { NonZeroUsize::new_unchecked(n - i) });
} else {
log::debug!("MountInfoIter::advance_to advanced to the {i}th table entry");
self.fwd_cursor = ptr;
}
}
1 => {
log::debug!("MountInfoIter::advance_to reached the end of `MountInfoIter`");
return Err(unsafe { NonZeroUsize::new_unchecked(n - i) });
}
code => {
log::debug!( "MountInfoIter::advance_to failed to advance to {i:?}th table entry. libmount::mnt_table_next_fs returned error code: {code:?}");
return Err(unsafe { NonZeroUsize::new_unchecked(n - i) });
}
}
}
Ok(())
}
}
impl<'table> Iterator for MountInfoIter<'table> {
type Item = &'table MountInfoEntry;
fn next(&mut self) -> Option<Self::Item> {
log::debug!("MountInfoIter::next getting next table entry");
let mut entry_ptr = MaybeUninit::<*mut libmount::libmnt_fs>::zeroed();
let result = unsafe {
libmount::mnt_table_next_fs(
self.table.inner,
self.fwd_iter.inner,
entry_ptr.as_mut_ptr(),
)
};
match result {
0 => {
let ptr = unsafe { entry_ptr.assume_init() };
// Per the documentation of `DoubleEndedIterator`
// "It is important to note that both back and forth work on the same range, and do not cross: iteration is over when they meet in the middle."
if self.have_iterators_met
|| (self.fwd_cursor != self.bwd_cursor && ptr == self.bwd_cursor)
{
log::debug!(
"MountInfoIter::next forward and backward iterators have met in the middle"
);
self.have_iterators_met = true;
None
} else {
log::debug!("MountInfoIter::next got next table entry");
self.fwd_cursor = ptr;
let entry = owning_ref_from_ptr!(self.table, MountInfoEntry, ptr);
Some(entry)
}
}
1 => {
log::debug!("MountInfoIter::next reached end of `MountInfoIter`");
None
}
code => {
log::debug!( "MountInfoIter::next failed to get next table entry. libmount::mnt_table_next_fs returned error code: {code:?}");
None
}
}
}
// Skips n-1 entries, and updates cursor.
fn nth(&mut self, n: usize) -> Option<Self::Item> {
log::debug!("MountInfoIter::nth getting {n}th table entry");
let mut result;
for i in 0..n {
let mut entry_ptr = MaybeUninit::<*mut libmount::libmnt_fs>::zeroed();
result = unsafe {
libmount::mnt_table_next_fs(
self.table.inner,
self.fwd_iter.inner,
entry_ptr.as_mut_ptr(),
)
};
match result {
0 => {
let ptr = unsafe { entry_ptr.assume_init() };
// Per the documentation of `DoubleEndedIterator`
// "It is important to note that both back and forth work on the same range, and do not cross: iteration is over when they meet in the middle."
if self.have_iterators_met
|| (self.fwd_cursor != self.bwd_cursor && ptr == self.bwd_cursor)
{
log::debug!(
"MountInfoIter::nth forward and backward iterators have met in the middle"
);
self.have_iterators_met = true;
return None;
} else {
log::debug!("MountInfoIter::nth got {i}th table entry");
self.fwd_cursor = ptr;
}
}
1 => {
log::debug!("MountInfoIter::nth reached the end of `MountInfoIter`");
return None;
}
code => {
log::debug!( "MountInfoIter::nth failed to get {i:?}th table entry. libmount::mnt_table_next_fs returned error code: {code:?}");
return None;
}
}
}
self.next()
}
}
impl<'table> DoubleEndedIterator for MountInfoIter<'table> {
fn next_back(&mut self) -> Option<Self::Item> {
log::debug!("MountInfoIter::next_back getting next table entry from the back");
let mut entry_ptr = MaybeUninit::<*mut libmount::libmnt_fs>::zeroed();
let result = unsafe {
libmount::mnt_table_next_fs(
self.table.inner,
self.bwd_iter.inner,
entry_ptr.as_mut_ptr(),
)
};
match result {
0 => {
let ptr = unsafe { entry_ptr.assume_init() };
// Per the documentation of `DoubleEndedIterator`
// "It is important to note that both back and forth work on the same range, and do not cross: iteration is over when they meet in the middle."
if self.have_iterators_met
|| (self.fwd_cursor != self.bwd_cursor && ptr == self.fwd_cursor)
{
log::debug!(
"MountInfoIter::next_back forward and backward iterators have met in the middle"
);
self.have_iterators_met = true;
None
} else {
log::debug!("MountInfoIter::next_back got next table entry");
self.bwd_cursor = ptr;
let entry = owning_ref_from_ptr!(self.table, MountInfoEntry, ptr);
Some(entry)
}
}
1 => {
log::debug!("MountInfoIter::next_back reached the beginning of `MountInfoIter`");
None
}
code => {
log::debug!( "MountInfoIter::next_back failed to get next table entry from the back. libmount::mnt_table_next_fs returned error code: {code:?}");
None
}
}
}
fn nth_back(&mut self, n: usize) -> Option<Self::Item> {
log::debug!("MountInfoIter::nth_back getting {n}th table entry from the back");
let mut result;
for i in 0..n {
let mut entry_ptr = MaybeUninit::<*mut libmount::libmnt_fs>::zeroed();
result = unsafe {
libmount::mnt_table_next_fs(
self.table.inner,
self.bwd_iter.inner,
entry_ptr.as_mut_ptr(),
)
};
match result {
0 => {
let ptr = unsafe { entry_ptr.assume_init() };
// Per the documentation of `DoubleEndedIterator`
// "It is important to note that both back and forth work on the same range, and do not cross: iteration is over when they meet in the middle."
if self.have_iterators_met
|| (self.fwd_cursor != self.bwd_cursor && ptr == self.fwd_cursor)
{
log::debug!(
"MountInfoIter::nth_back forward and backward iterators have met in the middle"
);
self.have_iterators_met = true;
return None;
} else {
log::debug!("MountInfoIter::nth_back got {i}th table entry from the back");
self.bwd_cursor = ptr;
}
}
1 => {
log::debug!("MountInfoIter::nth_back reached the beginning of `MountInfoIter`");
return None;
}
code => {
log::debug!( "MountInfoIter::nth_back failed to get {i:?}th table entry from the back. libmount::mnt_table_next_fs returned error code: {code:?}");
return None;
}
}
}
self.next_back()
}
}