Richard Stallman <[EMAIL PROTECTED]> writes:
> Or could one check the C code for "insert-file-contents"? Does it
> mark the buffer modified if 0 bytes were read.
>
> The code appears specifically to avoid marking the buffer modified
> if the file has zero size. I just did a test, inserting an empty
> file into a buffer this way. It did not mark the buffer modified
> and did not lock the file.
>
> Something we don't understand must be happening, and only you
> are in a position to debug it.
I have spent some time tracing the code of insert-file-contents. I do
not understand what it is trying to do, to be honest, but this is what
it **appears** to be doing: If the file it is trying to read has ZERO
bytes according to what stat() returns, it does the following:
----lines 176-181 of fileio.c
/* The file size returned from stat may be zero, but data
may be readable nonetheless, for example when this is a
file in the /proc filesystem. */
if (st.st_size == 0)
XSETINT (end, READ_BUF_SIZE);
---------
This has the effect of setting the amount to be read to non-zero.
Around line 707 it does
total = XINT (end) - XINT (beg);
setting total to something very much other than zero (some buffer
size), and in the next if statement (line 718)
if (NILP (visit) && total > 0)
prepare_to_modify_buffer (PT, PT, NULL);
which as far as I can tell calls lock_file on the underlying file.
Any other suggestions/ideas?
--Boris
PS. I can see the comment in fileio.c regarding /proc and can guess
that this sometimes might come in handy, but I do not see why reading
a regular zero-byte file should force a modification and/or locking of
the current buffer. But if I am right, I do not see how reading a
zero-byte file can EVER work right. Richard said he tried some casual
tests and it seems to work. I just tried creating a file qqqq in /tmp,
visiting it, and doing (insert-file-contents "/var/mail/whatever") and
lo and behold, a lock file for /tmp/qqqq showed up! Just tried it
again with /tmp/empty in place of /var/mail/whatever---same effect.
Does it mean that 0-size insertion is just broken on my machine
(Solaris 5.7, gcc 3.1)?
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