Lecture 111 - Implementing FSEEK in user land

nibblebits · nibblebits · commit 8886c648787d · 2025-08-11T10:49:53.000+01:00
diff --git a/PeachOS64Bit/programs/blank/blank.elf b/PeachOS64Bit/programs/blank/blank.elf
diff --git a/PeachOS64Bit/programs/shell/shell.elf b/PeachOS64Bit/programs/shell/shell.elf
diff --git a/PeachOS64Bit/programs/stdlib/build/file.o b/PeachOS64Bit/programs/stdlib/build/file.o
diff --git a/PeachOS64Bit/programs/stdlib/build/peachos.asm.o b/PeachOS64Bit/programs/stdlib/build/peachos.asm.o
diff --git a/PeachOS64Bit/programs/stdlib/src/file.c b/PeachOS64Bit/programs/stdlib/src/file.c
@@ -16,4 +16,9 @@ void fclose(int fd)
 int fread(void* buffer, size_t size, size_t count, long fd)
 {
     return peachos_fread(buffer, size, count, fd);
+}
+
+int fseek(int fd, int offset, int whence)
+{
+    return (int) peachos_fseek(fd, offset, whence);
 }
diff --git a/PeachOS64Bit/programs/stdlib/src/file.h b/PeachOS64Bit/programs/stdlib/src/file.h
@@ -7,5 +7,5 @@
 int fopen(const char* filename, const char* mode);
 void fclose(int fd);
 int fread(void* buffer, size_t size, size_t count, long fd);
-
+int fseek(int fd, int offset, int whence);
 #endif
diff --git a/PeachOS64Bit/programs/stdlib/src/peachos.asm b/PeachOS64Bit/programs/stdlib/src/peachos.asm
@@ -14,6 +14,7 @@ global peachos_exit:function
 global peachos_fopen:function
 global peachos_fclose:function
 global peachos_fread:function
+global peachos_fseek:function
 
 ; void print(const char* filename)
 print:
@@ -110,4 +111,14 @@ peachos_fread:
     push qword rdi ; buffer
     int 0x80  ; invoke kernel
     add rsp, 32 ; restore the stack
-    ret
+    ret
+
+; long peachos_fseek(long fd, long offset, long whence);
+peachos_fseek:
+    mov rax, 13 ; Command 13 fseek 
+    push qword rdx ; whence
+    push qword rsi ; offset
+    push qword rdi ; fd
+    int 0x80       ; invokes the kernel
+    add rsp, 24    ; restores the stack
+    ret            ; return
diff --git a/PeachOS64Bit/programs/stdlib/src/peachos.h b/PeachOS64Bit/programs/stdlib/src/peachos.h
@@ -35,5 +35,5 @@ void peachos_exit();
 int peachos_fopen(const char* filename, const char* mode);
 void peachos_fclose(size_t fd);
 long peachos_fread(void* buffer, size_t size, size_t count, long fd);
-
+long peachos_fseek(long fd, long offset, long whence);
 #endif
diff --git a/PeachOS64Bit/programs/stdlib/stdlib.elf b/PeachOS64Bit/programs/stdlib/stdlib.elf
diff --git a/PeachOS64Bit/src/isr80h/file.c b/PeachOS64Bit/src/isr80h/file.c
@@ -4,6 +4,14 @@
 #include "idt/idt.h"
 #include <stddef.h>
 #include <stdint.h>
+void* isr80h_command13_fseek(struct interrupt_frame* frame)
+{ 
+    long fd = (long) task_get_stack_item(task_current(), 0);
+    long offset = (long) task_get_stack_item(task_current(), 1);
+    long whence = (long) task_get_stack_item(task_current(), 2);
+
+    return (void*) (long) process_fseek(task_current()->process, fd, offset, whence);
+}
 
 void* isr80h_command12_fread(struct interrupt_frame* frame)
 {
diff --git a/PeachOS64Bit/src/isr80h/file.h b/PeachOS64Bit/src/isr80h/file.h
@@ -2,6 +2,7 @@
 #define KERNEL_ISR80H_FILE_H
 
 struct interrupt_frame;
+void* isr80h_command13_fseek(struct interrupt_frame* frame);
 void* isr80h_command12_fread(struct interrupt_frame* frame);
 void* isr80h_command11_fclose(struct interrupt_frame* frame);
 void* isr80h_command10_fopen(struct interrupt_frame* frame);
diff --git a/PeachOS64Bit/src/isr80h/isr80h.c b/PeachOS64Bit/src/isr80h/isr80h.c
@@ -20,4 +20,5 @@ void isr80h_register_commands()
     isr80h_register_command(SYSTEM_COMMAND10_FOPEN, isr80h_command10_fopen);
     isr80h_register_command(SYSTEM_COMMAND11_FCLOSE, isr80h_command11_fclose);
     isr80h_register_command(SYSTEM_COMMAND12_FREAD, isr80h_command12_fread);
+    isr80h_register_command(SYSTEM_COMMAND13_FSEEK, isr80h_command13_fseek);
 }
diff --git a/PeachOS64Bit/src/isr80h/isr80h.h b/PeachOS64Bit/src/isr80h/isr80h.h
@@ -16,6 +16,7 @@ enum SystemCommands
     SYSTEM_COMMAND10_FOPEN,
     SYSTEM_COMMAND11_FCLOSE,
     SYSTEM_COMMAND12_FREAD,
+    SYSTEM_COMMAND13_FSEEK,
 };
 
 void isr80h_register_commands();
diff --git a/PeachOS64Bit/src/task/process.c b/PeachOS64Bit/src/task/process.c
@@ -732,6 +732,20 @@ int process_validate_memory_or_terminate(struct process* process, void* virt_add
     }
     return res;
 }
+int process_fseek(struct process* process, int fd, int offset, FILE_SEEK_MODE whence)
+{
+    int res = 0;
+    struct process_file_handle* handle = process_file_handle_get(process, fd);
+    if (!handle)
+    {
+        res = -EIO;
+        goto out;
+    }
+
+    res = fseek(handle->fd, offset, whence);
+out:
+    return res;
+}
 int process_fread(struct process *process, void *virt_ptr, uint64_t size, uint64_t nmemb, int fd)
 {
     int res = 0;
diff --git a/PeachOS64Bit/src/task/process.h b/PeachOS64Bit/src/task/process.h
@@ -4,6 +4,7 @@
 #include <stdbool.h>
 
 #include "task.h"
+#include "fs/file.h"
 #include "config.h"
 
 #define PROCESS_FILETYPE_ELF 0
@@ -123,5 +124,6 @@ struct process_file_handle* process_file_handle_get(struct process* process, int
 int process_fopen(struct process* process, const char* path, const char* mode);
 int process_fclose(struct process* process, int fd);
 int process_fread(struct process* process, void* virt_ptr, uint64_t size, uint64_t nmemb, int fd);
+int process_fseek(struct process* process, int fd, int offset, FILE_SEEK_MODE whence);
 
 #endif

Original file line number	Diff line number	Diff line change
`@@ -16,4 +16,9 @@ void fclose(int fd)`
`16`	`16`	`int fread(void* buffer, size_t size, size_t count, long fd)`
`17`	`17`	`{`
`18`	`18`	`return peachos_fread(buffer, size, count, fd);`
	`19`	`+}`
	`20`	`+`
	`21`	`+int fseek(int fd, int offset, int whence)`
	`22`	`+{`
	`23`	`+ return (int) peachos_fseek(fd, offset, whence);`
`19`	`24`	`}`