Description

Trace

• SYSCALL_DEFINE3(open)
  • force_o_largefile()
    • Macro Returning true if we want to force the O_LARGEFILE (LFS) flag
  • do_sys_open()
    • build_open_flags()
      • Gets the access mode for the file based on given flags (ACC_MODE macro), e.g. O_RDONLY, O_WRONLY, O_RDWR
    • getname()
      • getname_flags()
        • Copies the filepath given from userspace to kernel space, returning a `filename` structure
    • do_filp_open()
      • set_nameidata()
        • Initializes the nameidata structure, which will point to the inode for the opened file
      • path_openat()
        • path_init()
          • Find start position of path
        • while(link_path_walk() && do_last())
          • Figures out path names, file permissions
          • Fills in the `file` struct
            • inode_<lock|unlock>()
            • audit_inode()
            • path_to_nameidata()
            • vfs_open()
              • Creates and fills an `inode` struct from the virtual filesystem for the given path
              • do_dentry_open()
                • dummy
          • terminate_walk()
      • putname()

Structures

• open_flags
• filename
• file
• nameidata
• inode

Test Code

Contents of file 'test.txt':

hello world

Code:

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

int main(void)
{
    char buffer[200];

    int fd = open("test.txt", O_RDONLY);
    if (fd < 0) {
        perror("Failed to open test.txt\n");
        return -1;
    }

    int amount_read = read(fd, buffer, 200);
    printf("Read %d bytes: %s\n", amount_read, buffer);

    close(fd);

    return 0;
}

Screenshot