Merge branch 'signed-seek' into 'master'

change seek sig to match posix - signed pos and result

See merge request redox-os/syscall!45

src/scheme/mod.rs

@@ -2,8 +2,10 @@ pub use self::scheme::Scheme;
 pub use self::scheme_mut::SchemeMut;
 pub use self::scheme_block::SchemeBlock;
 pub use self::scheme_block_mut::SchemeBlockMut;
+pub use self::seek::*;
 
 mod scheme;
 mod scheme_mut;
 mod scheme_block;
 mod scheme_block_mut;
+mod seek;

src/scheme/scheme.rs

@@ -16,7 +16,7 @@ pub trait Scheme {
             SYS_DUP => self.dup(packet.b, unsafe { slice::from_raw_parts(packet.c as *const u8, packet.d) }),
             SYS_READ => self.read(packet.b, unsafe { slice::from_raw_parts_mut(packet.c as *mut u8, packet.d) }),
             SYS_WRITE => self.write(packet.b, unsafe { slice::from_raw_parts(packet.c as *const u8, packet.d) }),
-            SYS_LSEEK => self.seek(packet.b, packet.c, packet.d),
+            SYS_LSEEK => self.seek(packet.b, packet.c as isize, packet.d).map(|o| o as usize),
             SYS_FCHMOD => self.fchmod(packet.b, packet.c as u16),
             SYS_FCHOWN => self.fchown(packet.b, packet.c as u32, packet.d as u32),
             SYS_FCNTL => self.fcntl(packet.b, packet.c, packet.d),
@@ -92,7 +92,7 @@ pub trait Scheme {
     }
 
     #[allow(unused_variables)]
-    fn seek(&self, id: usize, pos: usize, whence: usize) -> Result<usize> {
+    fn seek(&self, id: usize, pos: isize, whence: usize) -> Result<isize> {
         Err(Error::new(EBADF))
     }
 

src/scheme/seek.rs

+use core::cmp;
+use core::convert::TryFrom;
+use crate::error::*;
+use crate::flag::*;
+
+/// Helper for seek calls
+/// In most cases it's easier to use a usize to track the offset and buffer size internally,
+/// but the seek interface uses isize.  This wrapper ensures EOVERFLOW errors are returned
+/// as appropriate if the value in the usize can't fit in the isize.
+pub fn calc_seek_offset_usize(cur_offset: usize, pos: isize, whence: usize, buf_len: usize) -> Result<isize> {
+    let cur_offset = isize::try_from(cur_offset).or_else(|_| Err(Error::new(EOVERFLOW)))?;
+    let buf_len = isize::try_from(buf_len).or_else(|_| Err(Error::new(EOVERFLOW)))?;
+    calc_seek_offset_isize(cur_offset, pos, whence, buf_len)
+}
+
+/// Helper for seek calls
+/// Result is guaranteed to be positive.
+/// EOVERFLOW returned if the arguments would cause an overflow.
+/// EINVAL returned if the new offset is out of bounds.
+pub fn calc_seek_offset_isize(cur_offset: isize, pos: isize, whence: usize, buf_len: isize) -> Result<isize> {
+    let new_offset = match whence {
+        SEEK_CUR => pos.checked_add(cur_offset),
+        SEEK_END => pos.checked_add(buf_len),
+        SEEK_SET => Some(pos),
+        _ => None,
+    };
+
+    match new_offset {
+        Some(new_offset) if new_offset < 0 => Err(Error::new(EINVAL)),
+        Some(new_offset) => Ok(cmp::min(new_offset, buf_len)),
+        None => Err(Error::new(EOVERFLOW))
+    }
+}
\ No newline at end of file