relibc: make CLOCK_MONOTONIC_RAW a distinct id on Redox

CLOCK_MONOTONIC_RAW previously equalled CLOCK_MONOTONIC (both 4), which is
semantically true on Redox (the monotonic clock is already un-slewed) but
breaks portable code that switch()es on both — e.g. Mesa's intel_gem.c had two
case labels with the same value (compile error). Give it a distinct id (5) and
map it back to the monotonic clock (id 4) in clock_gettime()/clock_getres()
before hitting the kernel time scheme, restoring Linux-compatible semantics for
all consumers.

cargo check clean for x86_64-unknown-redox.

src/header/time/redox.rs

@@ -2,5 +2,9 @@ use crate::platform::types::c_int;
 
 pub const CLOCK_REALTIME: c_int = 1;
 pub const CLOCK_MONOTONIC: c_int = 4;
-// Redox's monotonic clock is the un-slewed hardware timer, so RAW is identical.
-pub const CLOCK_MONOTONIC_RAW: c_int = 4;
+// Redox's monotonic clock is already the un-slewed hardware timer, so RAW reads
+// the same underlying source. It MUST use a distinct id from CLOCK_MONOTONIC,
+// though, because portable code (e.g. Mesa's intel_gem) `switch`es on both and
+// two equal case values won't compile. clock_gettime()/clock_getres() map this
+// id back onto the monotonic clock (id 4) before hitting the kernel time scheme.
+pub const CLOCK_MONOTONIC_RAW: c_int = 5;

src/platform/redox/mod.rs

@@ -55,7 +55,8 @@ use crate::{
         sys_time::timezone,
         sys_utsname::{UTSLENGTH, utsname},
         time::{
-            CLOCK_MONOTONIC, CLOCK_REALTIME, TIMER_ABSTIME, itimerspec, timer_internal_t, timespec,
+            CLOCK_MONOTONIC, CLOCK_MONOTONIC_RAW, CLOCK_REALTIME, TIMER_ABSTIME, itimerspec,
+            timer_internal_t, timespec,
         },
         unistd::{F_OK, R_OK, SEEK_CUR, SEEK_END, SEEK_SET, W_OK, X_OK},
     },
@@ -307,7 +308,8 @@ unsafe { BRK_CUR = addr };
     fn clock_getres(clk_id: clockid_t, res: Option<Out<timespec>>) -> Result<()> {
         let path = match clk_id {
             CLOCK_REALTIME => "/scheme/time/1/getres",
-            CLOCK_MONOTONIC => "/scheme/time/4/getres",
+            // CLOCK_MONOTONIC_RAW shares the monotonic clock source on Redox.
+            CLOCK_MONOTONIC | CLOCK_MONOTONIC_RAW => "/scheme/time/4/getres",
             _ => return Err(Errno(EINVAL)),
         };
         let timerfd = FdGuard::open(path, syscall::O_RDONLY)?;
@@ -334,6 +336,15 @@ unsafe {
     }
 
     fn clock_gettime(clk_id: clockid_t, tp: Out<timespec>) -> Result<()> {
+        // CLOCK_MONOTONIC_RAW is a distinct clock id (so portable switch()es
+        // compile) but reads the same un-slewed monotonic source; libredox uses
+        // the id directly as the /scheme/time/<id> number, which only has 1 and
+        // 4, so translate RAW back to CLOCK_MONOTONIC here.
+        let clk_id = if clk_id == CLOCK_MONOTONIC_RAW {
+            CLOCK_MONOTONIC
+        } else {
+            clk_id
+        };
         libredox::clock_gettime(clk_id as usize, tp)?;
         Ok(())
     }