McAfee Interview Question for Software Engineer / Developers

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In Windows OS, the system call is implemented using system table and each call is assigned a number and they are dispatched based on this number when the context switch happens from user mode to kernel mode in NtxxxFile functions. The context switch happens using SYSENTER/SYSEXIT functions internally (I guess on intel processors). Kernel implements service table and using the index passed dispatches to appropriate system call.
The call is dispatched to IO manager but after prepending the path with \\?? or \\Global?? (depending on OS release). IO internally calls IOParseDevice which checks for security attributes and sends the request to object manager. Object manager in turn checks for volume object based on \\??\C: (assuming filename is c:\test.txt). Once it finds volume object it returns to IOParseDevice which searches for VPB to see if any FS is mounted on this volume. if there's then it creates file object and calls FS driver with file object. FS again checks for security and other parameters and returns success it it identifies the file belonging to its format. Object Manager while returning creates corresponding file handle and adds in process handle table. if FS returns failure then file object is deleted.if FS is not identified then mount process is initiated which identifies FS for given volume or returns error.
This is as per my understanding of windows (given in internals book).

- Anonymous October 04, 2011 | Flag Reply

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