# Mcafee interview questions and answers

Jan 7 • Placement • 13291 Views • 15 Comments on Mcafee interview questions and answers

Mcafee was founded in in 1987 by John Mcafee and has head office at Santa Clara California. Mcafee is in security software. McAfee provides the software solutions and the data protection, Database Security, Email and Web Securities and other software related issues. Being the part of this global organisation is an honor. For this, here are the McAfee Interview Questions and Answers which has been asked in the McAfee Recruitment process.

1. Normal bubble sort require 100sec to sort 10000 entries. What will be the input size if it will solve in 50 sec?
Ans = c*(10k)^2 => 100 sec
1/2*c*n^2 => 100*1/2 sec => 50 sec
c * (sqrt(1/2)*n)^2 => 50 sec
n1 => input size => sqrt(1/2) * floor(10k)
~ 0.7 * 10 k
=> 7k
= 7000

2. You are blindfolded and 20 coins are placed on the table in front of you. Out of them 10 coins have heads facing up and other tails. You are allowed to flip and move the coins. You should divide those coins into two sets such that one set contains 10 heads and other tails. You are allowed to only move or flip the coins
Ans = Can not be done exactly. But here is the try ->
flip 10 of them ,, not we have majority of heads or tails except we got all heads or all tails . move 10 of them . flip the other group of coins.

3. What are upper half and bottom half in device drivers.Why are they used?
Ans= Upper half and lower half are the terms related to interrupt handler and hardware devices only via drivers raise interrupts in this context , they asked u in form of device driver. Each device has to register its interrupt handler (which is the part of device driver. Now for devices which raise interrupt frequently or in case when same interrupt handler is used via devices so to increase the service performance driver designers design the handlers in such a way that whenever an interrupt occurs the OS does the most important part of handler “upper half” to respond to interrupt,create a data structure containing device specific data called “lower half” for later processing when CPU becomes available. This way interrupt handlers can be used in case when the interrupt raise frequency is high.

4. What is the mechanism for open(),read(),write() system calls how does the kernel implements them and what happens when a user space program uses
open(file,r) like this with arguments,how does kernel implement it.

Ans= 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.

5. On some architecture stack grows upwards and on some architecture stack grows downwards.How will you find out whether the stack is growing upwards or downwards?
Ans= void StackGrow()
{
int a[2];
printf(“%sn”,((&a[1]-&a[0])>0)?”upward”:”downward”);
}

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