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Kernel: Implement pread syscall

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The OpenFileDescription class already offers the necessary functionlity,
so implementing this was only a matter of following the structure for
`read` while handling the additional `offset` argument.
This commit is contained in:
Rodrigo Tobar 2021-10-12 21:13:28 +08:00 • committed by Andreas Kling
parent 8936b111a7
commit e1093c3403
3 changed files with 23 additions and 0 deletions
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21
Kernel/Syscalls/read.cpp
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@ -91,4 +91,25 @@ KResultOr<FlatPtr> Process::sys$read(int fd, Userspace<u8*> buffer, size_t size)
return TRY(description->read(user_buffer.value(), size));
}
KResultOr<FlatPtr> Process::sys$pread(int fd, Userspace<u8*> buffer, size_t size, off_t offset)
{
VERIFY_PROCESS_BIG_LOCK_ACQUIRED(this)
REQUIRE_PROMISE(stdio);
if (size == 0)
return 0;
if (size > NumericLimits<ssize_t>::max())
return EINVAL;
if (offset < 0)
return EINVAL;
dbgln_if(IO_DEBUG, "sys$pread({}, {}, {}, {})", fd, buffer.ptr(), size, offset);
auto description = TRY(open_readable_file_description(fds(), fd));
if (!description->file().is_seekable())
return EINVAL;
TRY(check_blocked_read(description));
auto user_buffer = UserOrKernelBuffer::for_user_buffer(buffer, size);
if (!user_buffer.has_value())
return EFAULT;
return TRY(description->read(user_buffer.value(), offset, size));
}
}