Kernel Programming Test (Solaris 2.x internals) Answers

1. How many LWPs must a process have to maximize its parallelism?

Answers:

• None

• Two

• It should be the same as the number of processors.

• It should be a factor of the available RAM.

2. Which of the following interfaces is used by the driver to signal the completion of an IO initiated by a strategy call?

Answers:

• biowait

• cv_broadcast

• biodone

• cv_signal

3. What does the vfs_vnodecovered field of a vfs structure indicate?

Answers:

• It points to the mounted on directory's vnode structure.

• It points to the root inode of the filesystem.

• It points to the root directory of the parent filesystem.

• It points to the vfs structure of the parent filesystem.

4. Which of the following commands can be used to examine and delete kernel breakpoints?

Answers:

• $b, :d

• ::break, ::delete

• $b, ::delete

• display break, delete break

5. Which of the following structures keeps track of the positional offset within the file where the next IO is to be performed?

Answers:

• struct file

• struct vnode

• struct inode

• struct proc

6. Which of the following structures describes the user initiated IOs?

Answers:

• struct buf

• struct file

• struct uio

• struct sio

7. Solaris rw locks are recursive locks. A thread that already holds a lock in the read mode can acquire the lock in the read mode

again.

Answers:

• True

• False

8. In which of the following driver interfaces should device instance specific resources be handled?

Answers:

• _init; _fini

• open; close

• attach; detach

• probe

9. Which of the following information must be tracked explicitly by a driver that allocates memory via kmem_alloc?

Answers:

• The address of the allocated memory.

• The size of the allocated memory.

• The alignment of the allocated memory.

• The thread that allocated the memory.

10. Is the solaris kernel fully preemtible?

Answers:

• Yes

• No

11. Which of the following operations results in the page cache being populated?

Answers:

• memory mapped IO

• read(2)/write(2) system calls

• opening a regular unix file.

• opening a socket.

12. Which of the following caches doesnot change its size dynamically on older solaris systems?

Answers:

• Page Cache

• Vnode Cache

• Inode Cache

• Buffer Cache

13. In which of the following contexts do callouts run?

Answers:

• User

• Kernel thread.

• LWP

• Interrupt.

14. Is the memory allocated by kmem_alloc paged?

Answers:

• Yes

• No

15. Which of the following kadb macros is useful in determining the panic address?

Answers:

• $<panic

• *panicstr

• $<msgbuf

• $r

16. What does the cv_wait_sig interface do?

Answers:

• It waits on the CV until the thread receives a specified external signal (sent via kill(2)).

• It waits on the CV until the thread receives a wakeup. It returns 0 if the thread receives an external signal (sent via kill(2)).

• It waits on the CV and ignores the specified signal but returns 0 if some other signal is received.

• It registers a call back with the kernel for the specified signal.

17. Why should floating point operations be avoided in drivers?

Answers:

• Because solaris does not support floating point operations at all.

• Because the sparc hardware does not support floating point operations.

• Because the kernel does not support floating point operations.

• Because they are expensive to perform.

18. Which of the following cache entries need to be purged/invalidated if a file is deleted?

Answers:

• DNLC

• Page Cache

• Buffer Cache

• Inode Cache

19. What is the correct way of deinitializing a mutex on solaris?

Answers:

• mutex_deinit(lock pointer)

• mutex_destroy(lock pointer)

• mutex_deinitialize(lock pointer)

• lockpointer-mutex_deinit()

20. What are the basic mutex operations supported by the solaris operating system?

Answers:

• Initializing and deinitializing the mutex

• Exclusively locking and unlocking the mutex

• Reader writer locking semantics on the mutex

• Try acquire mutex exclusive

21. Which of the following interfaces are invoked by the OS to flush all data belonging to a filesystem to a disk?

Answers:

• VOP_FSYNC

• VFS_SYNC

• VOP_PUTPAGE

• VOP_WRITE

22. What does the VOP_INACTIVE interface do?

Answers:

• It drops the reference count on a vnode.

• It deletes all data associated with a vnode.

• It drops the reference count on a vnode and if required it deletes all data associated with a vnode.

• It increments the reference count on a vnode.

23. What does the v_vfsmountedhere field of a vnode indicate?

Answers:

• If set to 1, it indicates that a filesystem is mounted on that vnode.

• It points to the root vnode of the filesystem to which the vnode belongs.

• It points to the vfs structure of the mounted on filesystem.

• It points to the root vnode of the mounted on filesystem.

24. Which of the following commands prints out the kernel device tree?

Answers:

• ls

• drvconf

• prtconf

• devlinks

25. The OS guarantees that a thread blocked on a cv via a cv_wait call does not wakeup prematurely and hence does not need to re-check for the reason for blocking.

Answers:

• True

• False

26. Which of the following interfaces needs to be implemented for a filesystem to support swap files?

Answers:

• VOP_WRITE and VOP_READ

• VOP_GETPAGE and VOP_PUTPAGE

• VOP_MAP and VOP_UNMAP

• VOP_PAGEIO

27. Which of the following interfaces can be used to avert a thundering herd of waiters?

Answers:

• cv_broadcast

• cv_signal

• cv_wakeall

• cv_wakeone

28. Which of the following components is responsible for speeding up file paths to inode lookups?

Answers:

• Page Cache

• DNLC

• Buffer Cache

• Vnode Cache

29. Which of the following is pageable?

Answers:

• kernel stack.

• user addresses.

• kernel heap.

• kernel code.

30. In which of the following contexts does the solaris kernel handle interrupts?

Answers:

• User context.

• LWP context.

• On a separate interrupt stack without any special context.

• In a kernel thread context.

31. What is the significance of setting the kernel global variable 'kmem_flags' to '0xf'?

Answers:

• It turns on buffer redzone (write past end of buffer).

• It turns on freed buffer checking.

• It turns on allocator auditing.

• It turns on uninitialized data checking.

• All of the above

32. Which of the following sequences correctly builds the loadable module 'mymod'?

Answers:

• cc mymod.c

• cc -o mymod.o mymod.c; ld -o mymod mymod.o

• cc -D_KERNEL mymod.c

• cc -D_KERNEL -o mymod.o; ld -r -o mymod mymod.o

33. Which of the following calls fits in at 'statement xxx'

to produce correct results in the code snippet below?

mutex_enter(mutex pointer);

while (condition is false) {

cv_wait(cv pointer, mutex pointer);

}

statement xxx;

mutex_exit(mutex pointer);

Answers:

• mutex_enter(mutex pointer)

• mutex_exit(mutex_pointer)

• nothing needs to be done.

• cv_signal(cv pointer)

34. Which of the following locking sequences is correct?

Answers:

• rw_init; rw_enter; rw_destroy

• rw_enter; rw_destroy

• rw_init; rw_enter; rw_exit; rw_destroy

• rw_init; rw_tryenter; unconditional rw_exit; rw_destroy

35. What do the following mdb commands do?

::allocdby

::freedby

Answers:

• They are used to print the log of transactions on a particular memory location.

• They are used to print the log of transactions by a particular thread.

• They are used to print the slab cache that refers to the particular address.

• They are used to print the arenas that refer to the particular address.

36. Which of the following is true of memory allocated by kmem_alloc?

Answers:

• It is physical memory.

• It is virtual memory.

• It is pageable.

• It is a part of the global kernel heap.

37. On a solaris system with no special kmem_flag settings,

what happens when a thread running buggy code frees a buffer twice.

Answers:

• The results are unpredictable including a panic.

• The kernel fails the second kmem_free.

• The kernel kills the thread with a SEGFAULT.

• The second free is harmless as the kernel knows that the memory has already been freed.

38. Which of the following interfaces can be used by a driver interface routine to copy data from and to the user address space?

Answers:

• memcpy

• bcopy

• copyin;copyout

• memmove

39. Which of the following abstractions is the fundamental schedulable entity on a solaris machine?

Answers:

• User process.

• LWP.

• Kernel thread.

• Interrupt handler.

40. Which of the following adb/kadb commands can be used to determine the function which caused the panic?

Answers:

• $<msgbuf

• panic address?ia

• $r

• $C

41. Which of the following sets does a breakpoint at the start of the kernel function ufs_read?

Answers:

• ufs_read:b

• ufs_read!break

• ::break ufs_read

• ufs_read>break

42. Which of the following sparc instructions forms the basis of all other locking strategies?

Answers:

• lock

• ldstub

• movsb

• save

43. Can the mutex be locked by one kernel thread and unlocked by another kernel thread?

Answers:

• Yes

• No

44. What is the outcome if an interrupt handler needs to block on a resource?

Answers:

• The kernel will detect this situation and will panic the system.

• The system will hang.

• The interrupt handler will block until it can run again.

• None of the above.

45. Which of the following has the lowest scheduling latency?

Answers:

• User thread.

• Kernel thread.

• User Process.

• LWP.

46. Which of the following commands can be used to examine the panic stack trace?

Answers:

• $r

• $<msgbuf

• $C

• $<threadlist

47. Which of the following sparc instructions is employed before returning from a function to restore the original context?

Answers:

• restore

• pop

• revert

• ret

48. Which of the following kernel interfaces can be used by a driver interface like open to identify the specific device instance involved in the operation?

Answers:

• getmajor(dev_t)

• getminor(dev_t)

• open

• ((dev_t) dev) & 0xFFFF0000;

49. The memory allocated by kmem_alloc is private to the kernel thread that allocated it.

Answers:

• True

• False

50. Which of the following interfaces is the preferred way for drivers to log messages?

Answers:

• printf

• cmn_err

• dmesg

• log

51. How many times can a semaphore be acquired without blocking?

Answers:

• It depends on the count associated with the semaphore.

• 1

• 2

• 0

52. Which of the following firmware commands causes a kernel core file to be dumped to the dump device?

Answers:

• $sync

• sync

• dump

• $dump

53. What does the following kernel interface do?

rw_lock_held(lock pointer);

Answers:

• It checks if the lock is held in the read mode.

• It checks if the lock is held in the write mode.

• It does 'a' and locks it in the write mode.

• It does 'b' and locks it in the read mode.

54. Which of the following is true of the memory allocated by kmem_alloc?

Answers:

• It is double word aligned.

• It is pageable.

• It is zero initialized.

• Its availability is limited to the amount of physical memory.

55. Which of the following interfaces does the OS call to translate path names to vnodes?

Answers:

• VOP_LOOKUP

• VOP_READDIR

• VOP_GETPAGE

• VOP_READ

56. What is the driver configuration file for a 64 bit target module 'mymod'?

Answers:

• /kernel/drv/mymod.conf

• /kernel/drv/sparcv9/mymod.conf

• /etc/system

• /usr/lib/mymod.conf

57. The condition variable synchronization primitives need which of the following primitives to be employed by the client code to function correctly?

Answers:

• Reader-writer locks.

• Mutex

• Semaphore

• Spin lock

58. Which of the following kadb/adb commands prints the contents of the register set at a particular stack depth?

Answers:

• $<msgbuf

• $C

• $r

• $b

59. If there is contention between readers and writers on an rw lock, which of them are given preference over the other?

Answers:

• Readers

• Writers

• Neither (there is FCFS granting of locks).

• Both (there is one grant from either group).

60. Which of the following mechanisms enables solaris to support real time applications?

Answers:

• Hidden scheduling.

• Priority inheritance.

• Priority inversion.

• Interrupts.

61. Is the glock necessary if a filesystem does not implement the mmap interface?

Answers:

• Yes

• No

62. Is the thread allowed to perform any kind of blocking operation while holding a mutex?

Answers:

• Yes

• No

63. Which of the following kernel subsystems employs a semaphore for synchronization?

Answers:

• Inode Cache

• Buffer Cache

• Page Cache

• DNLC

64. What does the OS do when it detects a page fault on a valid address?

Answers:

• It calls the VOP_READ interface of the vnode to fetch the data.

• It calls the VOP_MMAP interface of the vnode to fetch the data.

• It calls the buffer cache get block interface to fetch the data.

• It calls VOP_GETPAGE interface of the vnode to fetch the data.

65. Which of the following kadb/adb macros can be used to examine the stack traces of all the kernel threads?

Answers:

• $<stack

• $<traceall

• $<threadlist

• $<msgbuf

66. The OS can unload a module automatically if needed.

Answers:

• True

• False

67. Which of the following kernel defined data types is involved in the interface calls to manipulate CVs?

Answers:

• kmutex_t

• kcondvar_t

• vnode_t

• page_t

68. Which of the following debuggers allow extensive customization and supports user written pluggable debugging modules?

Answers:

• adb

• dbx

• crash

• mdb

69. What is the command to boot into the kernel debugger (kadb) from an 'ok' prompt?

Answers:

• boot kadb

• kadb

• unix kadb

• go kadb

70. What happens if a driver running on a sparc processor tries to access a 32 bit quantity which is aligned on a 16 bit boundary?

Answers:

• The processor automatically handles this situation.

• The system panics.

• Such a driver code will not be compiled.

• Such a driver code will not be loaded.

71. What are the commands to load and unload the kernel module 'mymod'?

Answers:

• insmod mymod; rmmod mymod

• pkgadd mymod; pkgrm mymod

• modload mymod; modunload mymod

• modload mymod; modunload -i moduleid

72. What is the compiler option to generate a 64 bit binary loadable on a sparc machine?

Answers:

• -xarch=v5

• -xarch=v9

• -64

• -target=64

73. What is the kernel interface to initialize a reader writer lock?

Answers:

• readwrite_init(lock pointer)

• rw_initialize(lock pointer)

• rw_init(lock pointer)

• rw_enter(lock pointer)

74. Can the solaris semaphores be used in the interrupt context?

Answers:

• Yes

• No

75. What is the correct way of initializing a mutex on solaris?

Answers:

• mutex_init(lock pointer, lock name, type of mutex)

• mutex_init(lock pointer)

• mutex_enter(lock pointer)

• mutex_initialize(lock pointer)

76. On a sparc system, which of the register set of a calling function is passed on as input registers to the called function?

Answers:

• input

• output

• local

• global

77. What sequence of key strokes is required to trap into the kadb in a live session?

Answers:

• STOP-A on sun keyboards.

• send brk via a telnet session.

• CTRL-A on sun keyboards.

• tip b via a serial console session.

78. Which of the following abstractions enables a multi-threaded application to take advantage of the available parallelism?

Answers:

• User threads.

• LWP.

• Kernel threads.

• User processes.

79. Which of the following sequences involving a CV is correct if a thread wants to wait for an event?

Answers:

• cv_init; mutex_enter; cv_wait; mutex_exit; cv_destroy

• cv_init; cv_wait; cv_destroy

• cv_init; cv_signal; cv_destroy

• cv_init; cv_timedwait; cv_destroy

80. Which of the following is true if an interrupt thread needs to block on a resource?

Answers:

• Interrupt threads on solaris cannot block.

• They can be scheduled to run on a different processor once they are runnable.

• They are scheduled to run on the same processor.

• The system hangs.

81. Which of the following types of information is stored within the buffer cache?

Answers:

• Filesystem Metadata

• User Pages backed by files.

• Anonymous Pages.

• DNLC entries.

82. Which of the following interfaces to a block device driver does the filesystem use?

Answers:

• int strategy(struct vnode *);

• int strategy(struct buf *);

• void strategy(struct uio *);

• int strategy(struct file *);

83. Which of the following buffer structure fields specifies the direction of IO transfer, the transfer size and the virtual address of the data?

Answers:

• b_flags

• b_bcount

• b_un

• b_blkno

84. What does the VFS_ROOT interface do?

Answers:

• It takes a vnode and a vfs and markes (marks or makes?) the vnode as the root vnode for the filesystem.

• It returns the root vnode of the specified vfs.

• It returns the parent vnode of the specified vnode.

• It returns the parent vfs of the specified vfs.

85. Which of the following locks is used to serialize reads and writes on a vnode?

Answers:

• The global VFS lock.

• The locks on the page structures.

• The VOP_RWLOCK.

• The locks on the buffer structures.

86. Which of the following CV interfaces can be used to wakeup exactly one waiter?

Answers:

• cv_broadcast

• cv_wakeone

• cv_wakeall

• cv_signal

87. Which of the following does the OS use for caching user data?

Answers:

• Buffer Cache

• Inode Cache

• Page Cache

• DNLC

88. Where is the following memory allocation type typically

employed?

memp = kmem_alloc(size, KM_NOSLEEP);

Answers:

• In the user context code as a backend to malloc.

• In the kernel context where every place memory needs to be allocated.

• In the interrupt context.

• In the buffer cache.

89. Which of the following sparc instructions causes a register window context to be created?

Answers:

• ldstub

• save

• restore

• movrw

90. Following a panic and a core dump, what is done to recreate the core files for debugging?

Answers:

• Use dumpadm to create the core files.

• Use savecore to create the core files.

• Nothing needs to be done; the os guarantees that the core files are always saved.

• Use dd to move the core files from the dump device to the filesystem.

91. Which of the following interfaces is equivalent to acquiring a lock?

Answers:

• sema_v

• sema_p

• sema_init

• sema_lock

92. Which of the following interfaces must be implemented by every loadable driver?

Answers:

• _init; _fini

• _init; _fini; probe

• _init; _info; _fini

• _init; _fini; open; close

93. Is it possible to take a core dump of a live system?

Answers:

• Yes

• No

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