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Re: how to reading 0 byte files properly

From: Andreas Schwab
Subject: Re: how to reading 0 byte files properly
Date: Thu, 17 Nov 2022 11:15:50 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/28.2 (gnu/linux)

On Nov 17 2022, Binbin YE wrote:

> /* emacs/src/fileio.c:4587 */
> if (seekable || !NILP (end))
>   total = end_offset - beg_offset;
> else
>   /* For a special file, all we can do is guess.  */
>   total = READ_BUF_SIZE;
> ```
> Judging from the code, it assume the total size would be READ_BUF_SIZE

For a non-seekable file this is just a buffer size, see the read loop
later in the function (how_much stays zero then).

If the file is seekable, the important part is this:

          /* The file size returned from fstat may be zero, but data
             may be readable nonetheless, for example when this is a
             file in the /proc filesystem.  */
          if (end_offset == 0)
            end_offset = READ_BUF_SIZE;

Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
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