Fix RamFS readahead

kernel/src/fs/utils/page_cache.rs

@@ -306,8 +306,12 @@ impl ReadaheadState {
         for async_idx in window.readahead_range() {
             let mut async_page = Page::alloc()?;
             let pg_waiter = backend.read_page_async(async_idx, async_page.frame())?;
-            self.waiter.concat(pg_waiter);
+            if pg_waiter.nreqs() > 0 {
-            async_page.set_state(PageState::Uninit);
+                self.waiter.concat(pg_waiter);
+            } else {
+                // Some backends (e.g. RamFS) do not issue requests, but fill the page directly.
+                async_page.set_state(PageState::UpToDate);
+            }
             pages.put(async_idx, async_page);
         }
         Ok(())
@@ -394,9 +398,7 @@ impl PageCacheManager {
             if let PageState::Uninit = page.state() {
                 // Cond 2: We should wait for the previous readahead.
                 // If there is no previous readahead, an error must have occurred somewhere.
-                if ra_state.request_number() == 0 {
+                assert!(ra_state.request_number() != 0);
-                    return_errno!(Errno::EINVAL)
-                }
                 ra_state.wait_for_prev_readahead(&mut pages)?;
                 pages.get(&idx).unwrap().frame().clone()
             } else {

test/apps/mmap/mmap_readahead.c

@@ -0,0 +1,39 @@
+// SPDX-License-Identifier: MPL-2.0
+
+#include <sys/mman.h>
+#include <sys/fcntl.h>
+#include <unistd.h>
+
+#include "../network/test.h"
+
+#define FILE_NAME "/tmp/mmap_readahead.txt"
+
+#define PAGE_SIZE 4096
+#define NR_PAGES 16
+
+static char *addr;
+
+FN_SETUP(mmap_readahead)
+{
+	int fd;
+
+	fd = CHECK(open(FILE_NAME, O_RDWR | O_CREAT));
+	CHECK(unlink(FILE_NAME));
+
+	CHECK(ftruncate(fd, PAGE_SIZE * NR_PAGES));
+
+	addr = mmap(NULL, PAGE_SIZE * NR_PAGES, PROT_READ | PROT_WRITE,
+		    MAP_SHARED, fd, 0);
+	CHECK(addr == MAP_FAILED ? -1 : 0);
+}
+END_SETUP()
+
+FN_TEST(mmap_readahead)
+{
+	int i;
+
+	for (i = 0; i < NR_PAGES; ++i) {
+		TEST_RES(addr[i * PAGE_SIZE], _ret == 0);
+	}
+}
+END_TEST()

test/apps/scripts/process.sh

@@ -22,6 +22,7 @@ itimer/setitimer
 itimer/timer_create
 mmap/mmap_and_fork
 mmap/mmap_shared_filebacked
+mmap/mmap_readahead
 pthread/pthread_test
 pty/open_pty
 signal_c/parent_death_signal