What will happen when we invoke a system call and
say with an example of invoking a system call ?read? for a
device?

Answer Posted / kumar babu

• User process executes a syscall open a file.
• User process links to a c runtime library for open and
sets up the needed parameters in registers.
• A software trap is executed now and the operation switches
to the kernel mode.
- The kernel looks up the syscall vector to call "open"
- The kernel tables are modified to open the file.
- Return to the point of call with exit status.
• Return to the user process with value and status.
• The user process may resume now with modified status on
file or abort on error with exit status.

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