On Thu, 11 Jan 2007, Linus Torvalds wrote:
>
> That said, clearly something didn't check the error return of a write()
> call. Some of that got fixed up recently, so it might even be fixed in
> current git already.
I'm not convinced.
The "write_in_full()" logic is supposed to help people avoid problems, but
it *still* returns a success for a partial write.
Example of extreme breakage:
static int write_buffer(int fd, const void *buf, size_t len)
{
ssize_t size;
size = write_in_full(fd, buf, len);
if (!size)
return error("file write: disk full");
if (size < 0)
return error("file write error (%s)", strerror(errno));
return 0;
}
which is TOTAL GARBAGE, because the disk-full event might have happened in
the middle of the write, so "write_in_full()" might have returned 4096,
for example, even though the buffer length was much bigger.
I personally think write_in_full() is totally mis-designed. If you are
ready to handle partial writes, you should use "xwrite()". If you're not
ready to handle partial writes, you should either use "write_or_die()",
_or_ you should expect a partial write to at least return an error code
(which is how "write_buffer()" works).
But that's not how write_in_full() actually works. Write-in-full does not
return an error for a partial write, it returns the partial size.
Which is idiotic. It makes the function pointless. Just use xwrite() for
that.
I would suggest perhaps a patch like this.. And then you _really_ can
just do
if (write_in_full(fd, buf, len) < 0)
die("Not going to work: %s", strerror(errno));
and be happy.
Linus
---
diff --git a/write_or_die.c b/write_or_die.c
index a119e1d..f95299a 100644
--- a/write_or_die.c
+++ b/write_or_die.c
@@ -37,15 +37,14 @@ int write_in_full(int fd, const void *buf, size_t count)
{
const char *p = buf;
ssize_t total = 0;
- ssize_t written = 0;
while (count > 0) {
- written = xwrite(fd, p, count);
- if (written <= 0) {
- if (total)
- return total;
- else
- return written;
+ size_t written = xwrite(fd, p, count);
+ if (written < 0)
+ return -1;
+ if (!written) {
+ errno = ENOSPC;
+ return -1
}
count -= written;
p += written;
-
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