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insert-file-contents st_size cleanup

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* src/fileio.c (Finsert_file_contents): Store st_size,
not file_size_hint, into current_buffer->modtime_size,
since modtime_size is compared to a later st_size, not
to the actual file size.  Simplify buffer overflow detection
from file size, since this occurred only on regular files.
This commit is contained in:
Paul Eggert 2025-07-17 09:50:07 -07:00
parent 5485bda523
commit 8d83402edc
2 changed files with 18 additions and 27 deletions
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11
src/buffer.h
View file

@ -649,11 +649,12 @@ struct buffer
in no case complain about any mismatch on next save attempt. */
struct timespec modtime;
/* Size of the file when modtime was set. This is used to detect the
case where the file grew while we were reading it, so the modtime
is still the same (since it's rounded up to seconds) but we're actually
not up-to-date. -1 means the size is unknown. Only meaningful if
modtime is actually set. */
/* Size of the file when modtime was set. This is used to detect when
the file size changed while we were reading the file, but the
modtime is still the same (since it's truncated to clock resolution)
so we're actually not up-to-date. Meaningful only if it is
nonnegative and the modtime is actually set. Useful only on
platforms with coarse clock resolution. */
off_t modtime_size;
/* The value of text->modiff at the last auto-save. */

34
src/fileio.c
View file

@ -4107,8 +4107,9 @@ by calling `format-decode', which see. */)
restore_window_points needs the old character count. */
ptrdiff_t same_at_end_charpos = ZV;
/* A hint about the file size, or -1 if there is no hint. */
off_t file_size_hint = -1;
/* The size reported by fstat, or -1 if the file was not found or its
size is meaningless. */
off_t st_size = -1;
if (current_buffer->base_buffer && ! NILP (visit))
error ("Cannot do file visiting in an indirect buffer");
@ -4201,11 +4202,12 @@ by calling `format-decode', which see. */)
if (regular | memory_object)
{
file_size_hint = st.st_size;
st_size = st.st_size;
/* A negative size can happen on a platform that allows file
sizes greater than the maximum off_t value. */
if (file_size_hint < 0)
/* On some ancient platforms, a regular file with a negative size means
the actual file size is greater than the maximum off_t value.
Fail now rather than doing a lot of work and exhausting memory. */
if (st_size < 0)
buffer_overflow ();
}
@ -4256,7 +4258,7 @@ by calling `format-decode', which see. */)
This saves a lot of needless work before a buffer overflow.
If LIKELY_END is nonnegative, it is likely where we will stop reading.
We could read more (or less), if the file grows (or shrinks). */
off_t likely_end = min (end_offset, file_size_hint);
off_t likely_end = min (end_offset, st_size);
if (beg_offset < likely_end)
{
ptrdiff_t buf_bytes
@ -4303,9 +4305,7 @@ by calling `format-decode', which see. */)
do not use st_size or report any SEEK_END failure. */
static_assert (4 * 1024 < sizeof read_buf);
ptrdiff_t nread = emacs_full_read (fd, read_buf, 4 * 1024);
if (nread < 4 * 1024)
file_size_hint = nread;
else
if (4 * 1024 <= nread)
{
off_t tailoff = emacs_fd_lseek (fd, - 3 * 1024, SEEK_END);
if (tailoff < 0)
@ -4326,7 +4326,6 @@ by calling `format-decode', which see. */)
}
else if (0 <= nread)
{
file_size_hint = tailoff + nread;
nread += 1024;
if (4 * 1024 < nread)
{
@ -4480,8 +4479,6 @@ by calling `format-decode', which see. */)
if (nread < bytes_to_read)
{
file_size_hint = curpos + nread;
/* Data inserted from the file match the buffer's leading bytes,
so there's no need to replace anything. */
emacs_fd_close (fd);
@ -4521,8 +4518,6 @@ by calling `format-decode', which see. */)
if (!giveup_match_end)
{
file_size_hint = endpos;
/* Shrink the file's head if the file shrank to
be smaller than its head. */
if (endpos < same_at_start_pos)
@ -4569,7 +4564,6 @@ by calling `format-decode', which see. */)
if (nread < 0)
report_file_error ("Read error", orig_filename);
/* The file unexpectedly shrank. */
file_size_hint = curpos + nread;
giveup_match_end = true;
break;
}
@ -4686,7 +4680,6 @@ by calling `format-decode', which see. */)
inserted = 0; /* Bytes put into CONVERSION_BUFFER so far. */
unprocessed = 0; /* Bytes not processed in previous loop. */
file_size_hint = beg_offset;
while (true)
{
@ -4700,7 +4693,6 @@ by calling `format-decode', which see. */)
if (this == 0)
break;
file_size_hint += this;
BUF_TEMP_SET_PT (XBUFFER (conversion_buffer),
BUF_Z (XBUFFER (conversion_buffer)));
decode_coding_c_string (&coding, (unsigned char *) read_buf,
@ -4861,7 +4853,7 @@ by calling `format-decode', which see. */)
/* Ensure the gap is at least one byte larger than needed for the
estimated insertion, so that in the usual case we read
without reallocating. */
off_t inserted_estimate = min (end_offset, file_size_hint) - beg_offset;
off_t inserted_estimate = likely_end - beg_offset;
if (GAP_SIZE <= inserted_estimate)
{
ptrdiff_t growth;
@ -4958,8 +4950,6 @@ by calling `format-decode', which see. */)
}
}
file_size_hint = beg_offset + inserted;
/* Now we have either read all the file data into the gap,
or stop reading on I/O error or quit. If nothing was
read, undo marking the buffer modified. */
@ -5119,7 +5109,7 @@ by calling `format-decode', which see. */)
if (NILP (handler))
{
current_buffer->modtime = mtime;
current_buffer->modtime_size = file_size_hint;
current_buffer->modtime_size = st_size;
bset_filename (current_buffer, orig_filename);
}