The SYSCALL macro is used to define the entry point of syscall related userland function like open, read, write, etc.

There is no Linux like C library on xv6 that defines the system call wrapper functions like read/write/fork/etc in userland.

The SYSCALL macro is used to store the number of the system call in the eax register.

Only hardware interrupts execute via the trap() function, and the system calls execute via the syscall() function in xv6 kernel.

The assembly code is involved only in kernel code, in the execution of a system call on xv6.

Addition of a new system call requires adding an entry to vectors.S which defines entry points for system calls and also for hardware interrupts.

No directory entry was found for the file to be opened, hence an error

ilock is held on the inode, and hence it's an error if it is a directory

One of the sub-components on the given path name, was not a directory, hence it's an error

The last path component (which is a file, and not a directory) has been resolved, so release the lock (using iunlockput) and return

There was a syntax error in the pathname specified

One of the sub-components on the given path name, was a directory, but it was not supposed to be a directory, hence an error

One of the sub-components on the given path name, did not exist, hence it's an error

Returns the inode with reference count incremented

Returns the inode with inode-cache lock held

Returns the inode locked

Returns a free-inode , with dev+inode-number set, if not found in cache

Panics if inode does not exist in cache

Returns a valid inode if not found in cache

Returns an inode with given dev+inode-number from cache, if it exists in cache

Copy the on-disk inode into in-memory inode, if neeed

Mark the in-memory inode as valid, if needed

Take the sleeplock on the inode, always

Lock all the buffers of the file in memory

Get the inode from the inode-cache

Take the sleeplock on the inode, optionally

Read the inode from disk, if needed