[lldb-dev] File::Read does not read everything

[Zachary Turner via lldb-dev]

Can you upload a diff (with context) to phabricator and add lldb-commits as
a subscriber and myself / Greg as reviewers?

On Mon, Oct 17, 2016 at 4:59 PM Eugene Birukov via lldb-dev <
lldb-dev at lists.llvm.org> wrote:

> Here is what I am running now:
>
>
> diff --git a/source/Host/common/File.cpp b/source/Host/common/File.cpp
> index 89587a9..a4ac25e 100644
> --- a/source/Host/common/File.cpp
> +++ b/source/Host/common/File.cpp
> @@ -771,21 +771,34 @@ File::Read (void *buf, size_t &num_bytes, off_t
> &offset)
>      int fd = GetDescriptor();
>      if (fd != kInvalidDescriptor)
>      {
> -        ssize_t bytes_read = -1;
> -        do
> +        size_t bytes_left = num_bytes;
> +        num_bytes = 0;
> +        char *pos = (char*)buf;
> +        while (bytes_left > 0)
>          {
> -            bytes_read = ::pread (fd, buf, num_bytes, offset);
> -        } while (bytes_read < 0 && errno == EINTR);
> +            ssize_t bytes_read = -1;
> +            do
> +            {
> +                bytes_read = ::pread (fd, pos, bytes_left, offset);
> +            } while (bytes_read < 0 && errno == EINTR);
>
> -        if (bytes_read < 0)
> -        {
> -            num_bytes = 0;
> -            error.SetErrorToErrno();
> -        }
> -        else
> -        {
> -            offset += bytes_read;
> -            num_bytes = bytes_read;
> +            if (bytes_read < 0)
> +            {
> +                num_bytes = 0;
> +                error.SetErrorToErrno();
> +                break;
> +            }
> +            else if (bytes_read == 0)
> +            {
> +                break;
> +            }
> +            else
> +            {
> +                offset += bytes_read;
> +                num_bytes += bytes_read;
> +                bytes_left -= bytes_read;
> +                pos += bytes_read;
> +            }
>          }
>      }
>      else
>
>
>
> Sent from Outlook <http://aka.ms/weboutlook>
>
>
> ------------------------------
> *From:* Greg Clayton <gclayton at apple.com>
> *Sent:* Monday, October 17, 2016 12:39 PM
> *To:* Eugene Birukov
> *Cc:* LLDB
> *Subject:* Re: [lldb-dev] File::Read does not read everything
>
> It is probably best to make the code loop as long as "bytes_reads > 0" and
> we haven't read "num_bytes" yet. The darwin kernel has a INT32_MAX read
> size which gets set to MAX_READ_SIZE, but we need to do that because if you
> try to read more than that it reads nothing. So MAX_READ_SIZE is more for
> the case where the read will outright fail if given a byte size that is too
> large. Feel free to submit a patch that can keep calling pread correctly in
> a loop as long as bytes_read > 0.
>
> Greg
>
> > On Oct 17, 2016, at 12:20 PM, Eugene Birukov via lldb-dev <
> lldb-dev at lists.llvm.org> wrote:
> >
> > Hello,
> >
> > I am using LLDB 3.9 on Linux Ubuntu. I am loading a 5GiB core which is
> located on Windows file share mounted on Linux via mount.cifs. I see that
> we successfully allocated memory and are trying to fill it in one read.
> Unfortunately pread returns 2GiB and we never check for short read here.
> >
> > I think we could combine this code with previous block "#if defined
> (MAX_READ_SIZE)" if we simply check for short read here (bytes_read too
> small) and loop until all the buffer is filled.
> >
> > Thanks,
> > Eugene
> >
> > #ifndef _WIN32
> >     int fd = GetDescriptor();
> >     if (fd != kInvalidDescriptor)
> >     {
> >         ssize_t bytes_read = -1;
> >         do
> >         {
> >             bytes_read = ::pread (fd, buf, num_bytes, offset);
> >         } while (bytes_read < 0 && errno == EINTR);
> >
> >         if (bytes_read < 0)
> >         {
> >             num_bytes = 0;
> >             error.SetErrorToErrno();
> >         }
> >         else
> >         {
> >             offset += bytes_read;
> >             num_bytes = bytes_read;
> >         }
> >     }
> >
> > Sent from Outlook
> > _______________________________________________
> > lldb-dev mailing list
> > lldb-dev at lists.llvm.org
> > http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev
>
> _______________________________________________
> lldb-dev mailing list
> lldb-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/lldb-dev/attachments/20161018/6d0f0dd1/attachment.html>