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Re: [Qemu-devel] [PATCH 1/2] elf-ops.h: Map into memory the ELF to load
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH 1/2] elf-ops.h: Map into memory the ELF to load |
Date: |
Tue, 23 Jul 2019 11:49:13 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 |
On 23/07/19 11:42, Stefano Garzarella wrote:
> "If writable is TRUE, the mapped buffer may be modified, otherwise it is an
> error to modify the mapped buffer. Modifications to the buffer are not visible
> to other processes mapping the same file, and are not written back to the
> file."
>
> I don't know what "error" means, but reading the second part I thought
> the changes in that case were only visible at the current process.
My reading would be that the second part applies to the writable==TRUE
case. In fact, the glib source code agrees:
file->contents = (gchar *) mmap (NULL, file->length,
writable ? PROT_READ|PROT_WRITE : PROT_READ,
MAP_PRIVATE, fd, 0);
meaning that we could after all just use writable == true.
Paolo
> I'll test it to understand better the behavior. If we can't touch it, then we
> have to make a copy in these cases.
>
>> (We can't get out of this by just passing writable=true, because
>> we definitely don't want to be writing back to the underlying file.)
> Yes, I agree.
[Qemu-devel] [PATCH 2/2] hw/i386/pc: Map into memory the initrd, Stefano Garzarella, 2019/07/23