kernel+libc: Add the lseek() syscall, and fseek, ftell, rewind, fsetpos, and fgetpos

kernel/src/sys/file.cpp

@@ -3,6 +3,9 @@
 #include "memory/MemoryManager.h"
 #include "sys/Syscall.h"
 #include "thread/Scheduler.h"
+#include <bits/seek.h>
+#include <luna/SafeArithmetic.h>
+#include <sys/types.h>
 
 Result<u64> sys_read(Registers*, SyscallArgs args)
 {
@@ -49,3 +52,34 @@ Result<u64> sys_write(Registers*, SyscallArgs args)
 
     return nwritten;
 }
+
+Result<u64> sys_lseek(Registers*, SyscallArgs args)
+{
+    int fd = (int)args[0];
+    off_t offset = (long)args[1];
+    int whence = (int)args[2];
+
+    if (fd < 0 || fd >= FD_MAX) return err(EBADF);
+
+    Thread* current = Scheduler::current();
+
+    Option<FileDescriptor>& descriptor = current->fd_table->fds[fd];
+
+    if (!descriptor.has_value()) return err(EBADF);
+
+    off_t new_offset;
+
+    switch (whence)
+    {
+    case SEEK_SET: new_offset = offset; break;
+    case SEEK_CUR: new_offset = TRY(safe_add((long)descriptor->offset, offset)); break;
+    case SEEK_END: todo();
+    default: return err(EINVAL);
+    }
+
+    if (new_offset < 0) return err(EINVAL);
+
+    descriptor->offset = (usize)new_offset;
+
+    return (u64)new_offset;
+}

libc/include/bits/seek.h

@@ -0,0 +1,10 @@
+/* bits/seek.h: SEEK_* constants for lseek() and fseek(). */
+
+#ifndef _BITS_SEEK_H
+#define _BITS_SEEK_H
+
+#define SEEK_SET 0
+#define SEEK_CUR 1
+#define SEEK_END 2
+
+#endif

libc/include/stdio.h

@@ -3,6 +3,7 @@
 #ifndef _STDIO_H
 #define _STDIO_H
 
+#include <bits/seek.h>
 #include <stdarg.h>
 #include <sys/types.h>
 
@@ -13,7 +14,6 @@ typedef struct
     int _eof;
 } FILE;
 
-#define SEEK_SET 0
 #define EOF -1
 
 extern FILE* stderr;
@@ -38,8 +38,20 @@ extern "C"
     /* Write arbitrarily sized items to a stream. */
     size_t fwrite(const void* buf, size_t size, size_t nmemb, FILE* stream);
 
-    int fseek(FILE*, long, int);
+    /* Move the file position. Clears the end-of-file indicator on success. */
-    long ftell(FILE*);
+    int fseek(FILE* stream, long offset, int whence);
+
+    /* Return the current file position. */
+    long ftell(FILE* stream);
+
+    /* Rewind the file position and clear the error and end-of-file indicators. */
+    void rewind(FILE* stream);
+
+    /* Save the current file position. */
+    int fgetpos(FILE* stream, fpos_t* pos);
+
+    /* Restore a file position. */
+    int fsetpos(FILE* stream, const fpos_t* pos);
 
     /* Return whether the error indicator was set in stream. */
     int ferror(FILE* stream);

libc/include/sys/types.h

@@ -13,5 +13,8 @@ typedef __i64_t ssize_t;
 typedef __i64_t time_t;
 typedef __u16_t mode_t;
 typedef __u64_t useconds_t;
+typedef __i64_t off_t;
+
+typedef off_t fpos_t;
 
 #endif

libc/include/unistd.h

@@ -6,6 +6,7 @@
 #define __need_NULL
 #include <stddef.h>
 
+#include <bits/seek.h>
 #include <stdint.h>
 #include <sys/types.h>
 
@@ -41,6 +42,9 @@ extern "C"
     /* Write bytes to a file descriptor. */
     ssize_t write(int fd, const void* buf, size_t size);
 
+    /* Modify a file descriptor's offset. */
+    off_t lseek(int fd, off_t offset, int whence);
+
 #ifdef __cplusplus
 }
 #endif

libc/src/stdio.cpp

@@ -75,6 +75,44 @@ extern "C"
         return (size_t)nwrite / size;
     }
 
+    int fseek(FILE* stream, long offset, int whence)
+    {
+        long result = lseek(stream->_fd, offset, whence);
+        if (result < 0) return -1;
+
+        // man fseek(3): A successful call to the fseek() function clears the end-of-file indicator for the stream.
+        stream->_eof = 0;
+
+        return 0;
+    }
+
+    long ftell(FILE* stream)
+    {
+        return lseek(stream->_fd, 0, SEEK_CUR);
+    }
+
+    void rewind(FILE* stream)
+    {
+        lseek(stream->_fd, 0, SEEK_SET);
+
+        clearerr(stream);
+    }
+
+    int fgetpos(FILE* stream, fpos_t* pos)
+    {
+        long offset = ftell(stream);
+        if (offset < 0) return -1;
+
+        *pos = offset;
+
+        return 0;
+    }
+
+    int fsetpos(FILE* stream, const fpos_t* pos)
+    {
+        return fseek(stream, *pos, SEEK_SET);
+    }
+
     int ferror(FILE* stream)
     {
         return stream->_err;

libc/src/unistd.cpp

@@ -60,4 +60,10 @@ extern "C"
         long rc = syscall(SYS_write, fd, buf, size);
         __errno_return(rc, ssize_t);
     }
+
+    off_t lseek(int fd, off_t offset, int whence)
+    {
+        long rc = syscall(SYS_lseek, fd, offset, whence);
+        __errno_return(rc, off_t);
+    }
 }

libluna/include/luna/Syscall.h

@@ -2,7 +2,7 @@
 
 #define enumerate_syscalls(_e)                                                                                         \
     _e(exit) _e(console_write) _e(clock_gettime) _e(allocate_memory) _e(deallocate_memory) _e(usleep) _e(open)         \
-        _e(close) _e(read) _e(getpid) _e(write)
+        _e(close) _e(read) _e(getpid) _e(write) _e(lseek)
 
 enum Syscalls
 {