Support SEEK_DATA and SEEK_HOLE for lseek (#486)

* Support `SEEK_DATA` and `SEEK_HOLE` for `lseek`

* Add `sparse` support to `libc` backend

* Do not use `std::io::Seekfrom`

* Remove `std::io::SeekFrom` from tests

* Remove `staged_api`

* Add more `cfg`

* Re-enable `seek_from` on Windows

* Enable for all supported OSes

* Improve docs

Author: sharifhsn

src/backend/libc/fs/syscalls.rs

@@ -900,6 +900,20 @@ pub(crate) fn seek(fd: BorrowedFd<'_>, pos: SeekFrom) -> io::Result<u64> {
         }
         SeekFrom::End(offset) => (c::SEEK_END, offset),
         SeekFrom::Current(offset) => (c::SEEK_CUR, offset),
+        #[cfg(any(
+            target_os = "linux",
+            target_os = "solaris",
+            target_os = "freebsd",
+            target_os = "dragonfly",
+        ))]
+        SeekFrom::Data(offset) => (c::SEEK_DATA, offset),
+        #[cfg(any(
+            target_os = "linux",
+            target_os = "solaris",
+            target_os = "freebsd",
+            target_os = "dragonfly",
+        ))]
+        SeekFrom::Hole(offset) => (c::SEEK_HOLE, offset),
     };
     let offset = unsafe { ret_off_t(libc_lseek(borrowed_fd(fd), offset, whence))? };
     Ok(offset as u64)

src/backend/linux_raw/fs/syscalls.rs

@@ -37,7 +37,8 @@ use linux_raw_sys::general::stat as linux_stat64;
 use linux_raw_sys::general::{
     __kernel_fsid_t, __kernel_timespec, open_how, statx, AT_EACCESS, AT_FDCWD, AT_REMOVEDIR,
     AT_SYMLINK_NOFOLLOW, F_ADD_SEALS, F_GETFL, F_GETLEASE, F_GETOWN, F_GETPIPE_SZ, F_GETSIG,
-    F_GET_SEALS, F_SETFL, F_SETPIPE_SZ, SEEK_CUR, SEEK_END, SEEK_SET, STATX__RESERVED,
+    F_GET_SEALS, F_SETFL, F_SETPIPE_SZ, SEEK_CUR, SEEK_DATA, SEEK_END, SEEK_HOLE, SEEK_SET,
+    STATX__RESERVED,
 };
 #[cfg(target_pointer_width = "32")]
 use {
@@ -214,6 +215,20 @@ pub(crate) fn seek(fd: BorrowedFd<'_>, pos: SeekFrom) -> io::Result<u64> {
         }
         SeekFrom::End(offset) => (SEEK_END, offset),
         SeekFrom::Current(offset) => (SEEK_CUR, offset),
+        #[cfg(any(
+            target_os = "linux",
+            target_os = "solaris",
+            target_os = "freebsd",
+            target_os = "dragonfly",
+        ))]
+        SeekFrom::Data(offset) => (SEEK_DATA, offset),
+        #[cfg(any(
+            target_os = "linux",
+            target_os = "solaris",
+            target_os = "freebsd",
+            target_os = "dragonfly",
+        ))]
+        SeekFrom::Hole(offset) => (SEEK_HOLE, offset),
     };
     _seek(fd, offset, whence)
 }

src/io/mod.rs

@@ -20,7 +20,6 @@ mod poll;
 mod procfs;
 #[cfg(not(windows))]
 mod read_write;
-#[cfg(not(feature = "std"))]
 mod seek_from;
 #[cfg(not(windows))]
 mod stdio;
@@ -87,10 +86,7 @@ pub use read_write::{pread, pwrite, read, readv, write, writev, IoSlice, IoSlice
 pub use read_write::{preadv, pwritev};
 #[cfg(any(target_os = "android", target_os = "linux"))]
 pub use read_write::{preadv2, pwritev2, ReadWriteFlags};
-#[cfg(not(feature = "std"))]
 pub use seek_from::SeekFrom;
-#[cfg(feature = "std")]
-pub use std::io::SeekFrom;
 #[cfg(not(windows))]
 pub use stdio::{
     raw_stderr, raw_stdin, raw_stdout, stderr, stdin, stdout, take_stderr, take_stdin, take_stdout,

src/io/seek_from.rs

@@ -27,4 +27,30 @@ pub enum SeekFrom {
     /// to seek before byte 0.
     #[cfg_attr(staged_api, stable(feature = "rust1", since = "1.0.0"))]
     Current(#[cfg_attr(staged_api, stable(feature = "rust1", since = "1.0.0"))] i64),
+
+    /// Sets the offset to the current position plus the specified number of bytes,
+    /// plus the distance to the next byte which is not in a hole.
+    ///
+    /// If the offset is in a hole at the end of the file, the seek will produce
+    /// an `NXIO` error.
+    #[cfg(any(
+        target_os = "linux",
+        target_os = "solaris",
+        target_os = "freebsd",
+        target_os = "dragonfly",
+    ))]
+    Data(i64),
+
+    /// Sets the offset to the current position plus the specified number of bytes,
+    /// plus the distance to the next byte which is in a hole.
+    ///
+    /// If there is no hole past the offset, it will be set to the end of the file
+    /// i.e. there is an implicit hole at the end of any file.
+    #[cfg(any(
+        target_os = "linux",
+        target_os = "solaris",
+        target_os = "freebsd",
+        target_os = "dragonfly",
+    ))]
+    Hole(i64),
 }

tests/io/read_write.rs

@@ -96,8 +96,8 @@ fn test_readwrite_v() {
 #[test]
 fn test_readwrite() {
     use rustix::fs::{cwd, openat, seek, Mode, OFlags};
+    use rustix::io::SeekFrom;
     use rustix::io::{read, write};
-    use std::io::SeekFrom;
 
     let tmp = tempfile::tempdir().unwrap();
     let dir = openat(cwd(), tmp.path(), OFlags::RDONLY, Mode::empty()).unwrap();