Function sys_read 

pub fn sys_read(_fd: u64, _buf: &mut [u8]) -> SyscallResult<usize>

Read data from an open file descriptor.

Reads up to buf.len() bytes from the file descriptor into the provided buffer, starting at the file’s current offset. The file offset is advanced by the number of bytes read. Partial reads are possible and normal: the kernel may return fewer bytes than requested if fewer are available (e.g., near end-of-file or for device files).

A return value of Ok(0) indicates end-of-file (EOF): the current offset is at or past the end of the file and no more data can be read.

For special file descriptors: fd 0 (stdin) reads from the process’s standard input source (terminal or pipe).

Arguments

• fd - File descriptor returned by a prior call to sys_open. Must be opened with at least O_RDONLY or O_RDWR access.
• buf - Mutable buffer to read data into. The kernel reads at most buf.len() bytes. Must be non-empty.

Returns

• Ok(bytes_read) - The number of bytes actually read, which may be less than buf.len(). Returns Ok(0) at end-of-file.

Errors

• SyscallError::BadDescriptor - fd is not a valid open file descriptor.
• SyscallError::PermissionDenied - The file descriptor was not opened for reading.
• SyscallError::InvalidArgument - buf has zero length.
• SyscallError::IoError - An I/O error occurred reading from the underlying storage or device.

Examples

use veridian_kernel::pkg::sdk::syscall_api::{sys_close, sys_open, sys_read};

let fd = sys_open("/etc/hostname", 0x000).expect("open failed");
let mut buf = [0u8; 256];
let bytes = sys_read(fd, &mut buf).expect("read failed");
if bytes == 0 {
    // End of file reached
}
let data = &buf[..bytes];
sys_close(fd).expect("close failed");