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libio: Add a new fwrite test that evaluates partial writes 

Test if the file-position is correctly updated when fwrite tries to
flush its internal cache but is not able to completely write all items.

Reviewed-by: DJ Delorie <dj@redhat.com>
This commit is contained in:
Tulio Magno Quites Machado Filho 2025-01-28 15:37:44 -03:00
parent 596a61cf6b
commit 1515f74fd8
2 changed files with 234 additions and 0 deletions
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1
stdio-common/Makefile
View File

@ -264,6 +264,7 @@ tests := \
tst-fwrite-memstrm \
tst-fwrite-overflow \
tst-fwrite-pipe \
tst-fwrite-pos \
tst-fwrite-ro \
tst-getline \
tst-getline-enomem \

233
stdio-common/tst-fwrite-pos.c Normal file
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@ -0,0 +1,233 @@
/* Test if fwrite returns consistent values on partial writes.
Copyright (C) 2025 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <errno.h>
/* stdio.h provides BUFSIZ, which is the size of fwrite's internal buffer. */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <support/check.h>
#include <support/fuse.h>
#include <support/support.h>
#include <support/xstdio.h>
#include <support/temp_file.h>
/* Length of the buffer in bytes. */
#define INBUF_SIZE (BUFSIZ)
/* Amount of bytes written to fwrite's internal cache that trigger a
flush. */
#define CACHE_THRESHOLD (BUFSIZ / 2)
#define ITERATIONS 1000
/* Maximum number of bytes written during a partial write. */
#define PARTIAL_BYTES 4
#define EXPECT_EVENT(opcode, state, expected_state) \
{ \
if (state != expected_state) \
{ \
char *s = support_fuse_opcode (opcode); \
FAIL ("unexpected event %s at state %d", s, state); \
free (s); \
} \
}
/* The goal of this test is to check that file position of a file stream is
correctly updated when write () returns a partial write.
The file system simulates pseudorandom partial writes while the test is
running.
Meanwhile the main thread calls fwrite () with a large object first and
small objects later. The usage of a large enough object ensures that
fwrite's internal cache is full enough, without triggering a write to file.
Subsequent calls to fwrite are guaranteed to trigger a write to file. */
static void
fuse_thread (struct support_fuse *f, void *closure)
{
struct fuse_in_header *inh;
int state = 0;
while ((inh = support_fuse_next (f)) != NULL)
{
{
char *opcode = support_fuse_opcode (inh->opcode);
printf ("info: (T) event %s(%llu) len=%u nodeid=%llu\n",
opcode, (unsigned long long int) inh->unique, inh->len,
(unsigned long long int) inh->nodeid);
free (opcode);
}
/* Handle mountpoint and basic directory operation for the root (1). */
if (support_fuse_handle_mountpoint (f)
|| (inh->nodeid == 1 && support_fuse_handle_directory (f)))
continue;
switch (inh->opcode)
{
case FUSE_LOOKUP:
EXPECT_EVENT (inh->nodeid, state, 0);
state++;
support_fuse_reply_error (f, ENOENT);
break;
case FUSE_CREATE:
EXPECT_EVENT (inh->nodeid, state, 1);
state++;
struct fuse_entry_out *entry;
struct fuse_open_out *open;
support_fuse_prepare_create (f, 2, &entry, &open);
entry->attr.mode = S_IFREG | 0600;
support_fuse_reply_prepared (f);
break;
case FUSE_GETXATTR:
/* We don't need to support extended attributes in this test. */
support_fuse_reply_error (f, ENOSYS);
break;
case FUSE_GETATTR:
/* Happens after open. */
if (inh->nodeid == 2)
{
struct fuse_attr_out *out = support_fuse_prepare_attr (f);
out->attr.mode = S_IFREG | 0600;
out->attr.size = 0;
support_fuse_reply_prepared (f);
}
else
support_fuse_reply_error (f, ENOENT);
break;
case FUSE_WRITE:
if (inh->nodeid == 2)
{
struct fuse_write_out out;
if (state > 1 && state < ITERATIONS + 2)
{
/* The 2nd and subsequent calls to fwrite () trigger a
flush of fwrite's internal cache. Simulate a partial
write of up to PARTIAL_BYTES bytes. */
out.padding = 0;
out.size = 1 + rand () % PARTIAL_BYTES,
state++;
support_fuse_reply (f, &out, sizeof (out));
}
else if (state >= ITERATIONS + 2)
{
/* This request is expected to come from fflush (). Copy
all the data successfully. This may be executed more
than once. */
struct fuse_write_in *p = support_fuse_cast (WRITE, inh);
out.padding = 0;
out.size = p->size,
state++;
support_fuse_reply (f, &out, sizeof (out));
}
else
support_fuse_reply_error (f, EIO);
}
else
support_fuse_reply_error (f, EIO);
break;
case FUSE_FLUSH:
case FUSE_RELEASE:
TEST_COMPARE (inh->nodeid, 2);
support_fuse_reply_empty (f);
break;
default:
FAIL ("unexpected event %s", support_fuse_opcode (inh->opcode));
support_fuse_reply_error (f, EIO);
}
}
}
static int
do_test (void)
{
char *in;
int i;
size_t written;
_Static_assert (CACHE_THRESHOLD <= INBUF_SIZE,
"the input buffer must be larger than the cache threshold");
/* Avoid filling up fwrite's cache. */
_Static_assert (CACHE_THRESHOLD - 1 + PARTIAL_BYTES * ITERATIONS <= BUFSIZ,
"fwrite's cache must fit all data written");
support_fuse_init ();
struct support_fuse *fs = support_fuse_mount (fuse_thread, NULL);
/* Create and open a temporary file in the fuse mount point. */
char *fname = xasprintf ("%s/%sXXXXXX", support_fuse_mountpoint (fs),
"tst-fwrite-fuse");
int fd = mkstemp (fname);
TEST_VERIFY_EXIT (fd != -1);
FILE *f = fdopen (fd, "w");
TEST_VERIFY_EXIT (f != NULL);
/* Allocate an input array that will be written to the temporary file. */
in = xmalloc (INBUF_SIZE);
for (i = 0; i < INBUF_SIZE; i++)
in[i] = i % 0xff;
/* Ensure the file position indicator is at the beginning of the stream. */
TEST_COMPARE (ftell (f), 0);
/* Try to fill as most data to the cache of the file stream as possible
with a single large object.
All data is expected to be written to the cache.
No errors are expected from this. */
TEST_COMPARE (fwrite (in, CACHE_THRESHOLD - 1, 1, f), 1);
TEST_COMPARE (ferror (f), 0);
written = CACHE_THRESHOLD - 1;
/* Ensure the file position indicator advanced correctly. */
TEST_COMPARE (ftell (f), written);
for (i = 0; i < ITERATIONS; i++)
{
/* Write an extra object of size PARTIAL_BYTES that triggers a write to
disk. Our FS will write at most PARTIAL_BYTES bytes to the file
instead of all the data. By writting PARTIAL_BYTES, we guarantee
the amount of data in the cache will never decrease below
CACHE_THRESHOLD.
No errors are expected. */
TEST_COMPARE (fwrite (in, PARTIAL_BYTES, 1, f), 1);
TEST_COMPARE (ferror (f), 0);
written += PARTIAL_BYTES;
/* Ensure the file position indicator advanced correctly. */
TEST_COMPARE (ftell (f), written);
}
/* Flush the rest of the data. */
TEST_COMPARE (fflush (f), 0);
TEST_COMPARE (ferror (f), 0);
/* Ensure the file position indicator was not modified. */
TEST_COMPARE (ftell (f), written);
/* In case an unexpected error happened, clear it before exiting. */
if (ferror (f))
clearerr (f);
xfclose (f);
free (fname);
free (in);
support_fuse_unmount (fs);
return 0;
}
#include <support/test-driver.c>