A pread system call

c126d25a · Silas Boyd-Wickizer · 53b19d0a · c126d25a · c126d25a · c126d25a
--- a/Makefile
+++ b/Makefile
@@ -92,7 +92,8 @@ UPROGS= \
 	_sleep \
 	_dirbench \
 	_usertests \
-	_lockstat
+	_lockstat \
+	_preadtest
 UPROGS := $(addprefix $(O)/, $(UPROGS))
 all: $(O)/kernel

--- a/preadtest.c
+++ b/preadtest.c
+#include "types.h"
+#include "stat.h"
+#include "fcntl.h"
+#include "user.h"
+#include "amd64.h"
+#define FSIZE (64 << 10)
+#define BSIZE 4096
+static char buf[BSIZE];
+int
+main(int ac, char **av)
+{
+  u64 t0, t1;
+  int fd;
+  int i;
+  fd = open("preadtest.x", O_CREATE|O_RDWR);
+  if (fd < 0)
+    die("open failed");
+  for (i = 0; i < FSIZE/BSIZE; i++)
+    if (write(fd, buf, BSIZE) != BSIZE)
+      die("write failed");
+  t0 = rdtsc();
+  for (i = 0; i < FSIZE; i+=BSIZE)
+    if (pread(fd, buf, BSIZE, i) != BSIZE)
+      die("pread failed");
+  t1 = rdtsc();
+  printf(1, "cycles %lu\n", t1 - t0);
+  exit();
+}
--- a/syscall.c
+++ b/syscall.c
@@ -174,6 +174,7 @@ extern long sys_socket(int, int, int);
 extern long sys_bind(int, void*, int);
 extern long sys_listen(int, int);
 extern long sys_accept(int, void*, void*);
+extern long sys_pread(int fd, void *ubuf, size_t count, off_t offset);
 #define SYSCALL(name) [SYS_##name] = (void*)sys_##name
@@ -206,6 +207,7 @@ static long (*syscalls[])(u64, u64, u64, u64, u64, u64) = {
  SYSCALL(bind),
  SYSCALL(listen),
  SYSCALL(accept),
+  SYSCALL(pread),
 };
 void

--- a/syscall.h
+++ b/syscall.h
@@ -27,3 +27,4 @@
 #define SYS_bind   26
 #define SYS_listen 27
 #define SYS_accept 28
+#define SYS_pread  29
--- a/sysfile.c
+++ b/sysfile.c
@@ -72,6 +72,27 @@ sys_read(void)
  return fileread(f, p, n);
 }
+ssize_t
+sys_pread(int fd, void *ubuf, size_t count, off_t offset)
+{
+  struct file *f;
+  int r;
+  if(fd < 0 || fd >= NOFILE || (f=myproc()->ofile[fd]) == 0)
+    return -1;
+  // XXX(sbw) assuming ubuf is ok
+  if(f->type == FD_INODE){
+    ilock(f->ip, 0);
+    if(f->ip->type == 0)
+      panic("fileread");
+    r = readi(f->ip, ubuf, offset, count);
+    iunlock(f->ip);
+    return r;
+  }
+  return -1;
+}
 long
 sys_write(void)
 {

--- a/types.h
+++ b/types.h
@@ -12,3 +12,8 @@ typedef uptr            paddr;
 // Page Map Entry (refers to any entry in any level)
 typedef u64             pme_t;
 typedef pme_t           pml4e_t;
+// POSIX types
+typedef s64             ssize_t;
+typedef u64             size_t;
+typedef u64             off_t;
--- a/user.h
+++ b/user.h
@@ -25,6 +25,7 @@ int uptime(void);
 int map(void *addr, int len);
 int unmap(void *addr, int len);
 void halt(void);
+ssize_t pread(int, void*, size_t, off_t);
 // ulib.c
 int stat(char*, struct stat*);

--- a/usys.S
+++ b/usys.S
@@ -36,3 +36,4 @@ SYSCALL(socket)
 SYSCALL(bind)
 SYSCALL(listen)
 SYSCALL(accept)
+SYSCALL(pread)