I have a question regarding mounting filesystem without giving filesystem type as argument to mount command: AFAIK when mount command is run to mount a FS the corresponding call made in kernel is "compat_sys_mount" as per kernel 2.6.36. Now compat_sys_kernel expects a filesystem "type" name as argument but in compat_sys_mount there is no check for "type" argument as NULL, now as part of this mount path do_kern_mount also called which uses the "type" argument to compat_sys_mount and finds out the corresponding file_system_type structure from the file_system_type structure list and if not matching structure is found it returns with error. 842 asmlinkage long compat_sys_mount(const char __user * dev_name, 843 const char __user * dir_name, 844 const char __user * type, unsigned long flags, <====== type argument to compat_sys_mount 845 const void __user * data) 846 { 847 char *kernel_type; 848 unsigned long data_page; 849 char *kernel_dev; 850 char *dir_page; 851 int retval; 852 853 retval = copy_mount_string(type, &kernel_type); 1098 do_kern_mount(const char *fstype, int flags, const char *name, void *data) 1099 { 1100 struct file_system_type *type = get_fs_type(fstype); <======= same type argument to search in list 1101 struct vfsmount *mnt; 1102 if (!type) <======= if the type name entry not found in list return ERRROR 1103 return ERR_PTR(-ENODEV); 1104 mnt = vfs_kern_mount(type, flags, name, data); 1105 if (!IS_ERR(mnt) && (type->fs_flags & FS_HAS_SUBTYPE) && 1106 !mnt->mnt_sb->s_subtype) 1107 mnt = fs_set_subtype(mnt, fstype); 1108 put_filesystem(type); 1109 return mnt; 1110 } Now my question is that if I don't provide FS type name to mount command how the FS gets mounted. Is there some other path for this code or if before calling compat_sys_mount i.e in user mode FS type is determined somehow? Regards, Piyush