[PING^2][PATCH v1.1] Fix offset computation for append+ mode on switching from read (BZ #16724)
Siddhesh Poyarekar
siddhesh@redhat.com
Fri Apr 11 09:40:00 GMT 2014
This fell off my ping radar, so...
Ping!
On Mon, Mar 24, 2014 at 09:21:38PM +0530, Siddhesh Poyarekar wrote:
> Ping!
>
> On Wed, Mar 19, 2014 at 12:37:55PM +0530, Siddhesh Poyarekar wrote:
> > The test case had a stupid error that got caught when I tested on
> > powerpc. Updated patch.
> >
> > The offset computation in write mode uses the fact that _IO_read_end
> > is kept in sync with the external file offset. This however is not
> > true when O_APPEND is in effect since switching to write mode ought to
> > send the external file offset to the end of file without making the
> > necessary adjustment to _IO_read_end.
> >
> > Hence in append mode, offset computation when writing should only
> > consider the effect of unflushed writes, i.e. from _IO_write_base to
> > _IO_write_ptr.
> >
> > Tested on x86_64 (and not x86_66 like I mentioned earlier ;)), i686,
> > s390 and ppc.
> >
> > Siddhesh
> >
> > [BZ #16724]
> > * libio/tst-ftell-append.c: New test case.
> > * libio/Makefile (tests): Add test case.
> > * libio/fileops.c (do_ftell): Don't trust _IO_read_end when in
> > append mode.
> > * libio/wfileops.c (do_ftell_wide): Likewise.
> >
> > ---
> > libio/Makefile | 3 +-
> > libio/fileops.c | 12 +++-
> > libio/tst-ftell-append.c | 169 +++++++++++++++++++++++++++++++++++++++++++++++
> > libio/wfileops.c | 13 +++-
> > 4 files changed, 192 insertions(+), 5 deletions(-)
> > create mode 100644 libio/tst-ftell-append.c
> >
> > diff --git a/libio/Makefile b/libio/Makefile
> > index 69c25c0..4bedfad 100644
> > --- a/libio/Makefile
> > +++ b/libio/Makefile
> > @@ -60,7 +60,8 @@ tests = tst_swprintf tst_wprintf tst_swscanf tst_wscanf tst_getwc tst_putwc \
> > tst-wmemstream1 tst-wmemstream2 \
> > bug-memstream1 bug-wmemstream1 \
> > tst-setvbuf1 tst-popen1 tst-fgetwc bug-wsetpos tst-fseek \
> > - tst-fwrite-error tst-ftell-partial-wide tst-ftell-active-handler
> > + tst-fwrite-error tst-ftell-partial-wide tst-ftell-active-handler \
> > + tst-ftell-append
> > ifeq (yes,$(build-shared))
> > # Add test-fopenloc only if shared library is enabled since it depends on
> > # shared localedata objects.
> > diff --git a/libio/fileops.c b/libio/fileops.c
> > index cf68dbf..204cfea 100644
> > --- a/libio/fileops.c
> > +++ b/libio/fileops.c
> > @@ -91,7 +91,9 @@ extern struct __gconv_trans_data __libio_translit attribute_hidden;
> >
> > The position in the buffer that corresponds to the position
> > in external file system is normally _IO_read_end, except in putback
> > - mode, when it is _IO_save_end.
> > + mode, when it is _IO_save_end and also when the file is in append mode,
> > + since switching from read to write mode automatically sends the position in
> > + the external file system to the end of file.
> > If the field _fb._offset is >= 0, it gives the offset in
> > the file as a whole corresponding to eGptr(). (?)
> >
> > @@ -966,6 +968,14 @@ do_ftell (_IO_FILE *fp)
> > /* Adjust for unflushed data. */
> > if (!was_writing)
> > offset -= fp->_IO_read_end - fp->_IO_read_ptr;
> > + /* We don't trust _IO_read_end to represent the current file offset when
> > + writing in append mode because the value would have to be shifted to
> > + the end of the file during a flush. Use the write base instead, along
> > + with the new offset we got above when we did a seek to the end of the
> > + file. */
> > + else if (append_mode)
> > + offset += fp->_IO_write_ptr - fp->_IO_write_base;
> > + /* For all other modes, _IO_read_end represents the file offset. */
> > else
> > offset += fp->_IO_write_ptr - fp->_IO_read_end;
> > }
> > diff --git a/libio/tst-ftell-append.c b/libio/tst-ftell-append.c
> > new file mode 100644
> > index 0000000..604dc03
> > --- /dev/null
> > +++ b/libio/tst-ftell-append.c
> > @@ -0,0 +1,169 @@
> > +/* Verify that ftell returns the correct value after a read and a write on a
> > + file opened in a+ mode.
> > + Copyright (C) 2014 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
> > + <http://www.gnu.org/licenses/>. */
> > +
> > +#include <stdio.h>
> > +#include <stdlib.h>
> > +#include <string.h>
> > +#include <errno.h>
> > +#include <unistd.h>
> > +#include <locale.h>
> > +#include <wchar.h>
> > +
> > +/* data points to either char_data or wide_data, depending on whether we're
> > + testing regular file mode or wide mode respectively. Similarly,
> > + fputs_func points to either fputs or fputws. data_len keeps track of the
> > + length of the current data and file_len maintains the current file
> > + length. */
> > +#define BUF_LEN 4
> > +static void *buf;
> > +static char char_buf[BUF_LEN];
> > +static wchar_t wide_buf[BUF_LEN];
> > +static const void *data;
> > +static const char *char_data = "abcdefghijklmnopqrstuvwxyz";
> > +static const wchar_t *wide_data = L"abcdefghijklmnopqrstuvwxyz";
> > +static size_t data_len;
> > +static size_t file_len;
> > +
> > +typedef int (*fputs_func_t) (const void *data, FILE *fp);
> > +fputs_func_t fputs_func;
> > +
> > +typedef void *(*fgets_func_t) (void *s, int size, FILE *stream);
> > +fgets_func_t fgets_func;
> > +
> > +static int do_test (void);
> > +
> > +#define TEST_FUNCTION do_test ()
> > +#include "../test-skeleton.c"
> > +
> > +static FILE *
> > +init_file (const char *filename)
> > +{
> > + FILE *fp = fopen (filename, "w");
> > + if (fp == NULL)
> > + {
> > + printf ("fopen: %m\n");
> > + return NULL;
> > + }
> > +
> > + int written = fputs_func (data, fp);
> > +
> > + if (written == EOF)
> > + {
> > + printf ("fputs failed to write data\n");
> > + fclose (fp);
> > + return NULL;
> > + }
> > +
> > + file_len = data_len;
> > +
> > + fclose (fp);
> > +
> > + fp = fopen (filename, "a+");
> > + if (fp == NULL)
> > + {
> > + printf ("fopen(a+): %m\n");
> > + return NULL;
> > + }
> > +
> > + return fp;
> > +}
> > +
> > +static int
> > +do_one_test (const char *filename)
> > +{
> > + FILE *fp = init_file (filename);
> > +
> > + if (fp == NULL)
> > + return 1;
> > +
> > + void *ret = fgets_func (buf, BUF_LEN, fp);
> > +
> > + if (ret == NULL)
> > + {
> > + printf ("read failed: %m\n");
> > + fclose (fp);
> > + return 1;
> > + }
> > +
> > + int written = fputs_func (data, fp);
> > +
> > + if (written == EOF)
> > + {
> > + printf ("fputs failed to write data\n");
> > + fclose (fp);
> > + return 1;
> > + }
> > +
> > + file_len += data_len;
> > +
> > + long off = ftell (fp);
> > +
> > + if (off != file_len)
> > + {
> > + printf ("Incorrect offset %ld, expected %zu\n", off, file_len);
> > + fclose (fp);
> > + return 1;
> > + }
> > + else
> > + printf ("Correct offset %ld after write.\n", off);
> > +
> > + return 0;
> > +}
> > +
> > +/* Run the tests for regular files and wide mode files. */
> > +static int
> > +do_test (void)
> > +{
> > + int ret = 0;
> > + char *filename;
> > + int fd = create_temp_file ("tst-ftell-append-tmp.", &filename);
> > +
> > + if (fd == -1)
> > + {
> > + printf ("create_temp_file: %m\n");
> > + return 1;
> > + }
> > +
> > + close (fd);
> > +
> > + /* Tests for regular files. */
> > + puts ("Regular mode:");
> > + fputs_func = (fputs_func_t) fputs;
> > + fgets_func = (fgets_func_t) fgets;
> > + data = char_data;
> > + buf = char_buf;
> > + data_len = strlen (char_data);
> > + ret |= do_one_test (filename);
> > +
> > + /* Tests for wide files. */
> > + puts ("Wide mode:");
> > + if (setlocale (LC_ALL, "en_US.UTF-8") == NULL)
> > + {
> > + printf ("Cannot set en_US.UTF-8 locale.\n");
> > + return 1;
> > + }
> > + fputs_func = (fputs_func_t) fputws;
> > + fgets_func = (fgets_func_t) fgetws;
> > + data = wide_data;
> > + buf = wide_buf;
> > + data_len = wcslen (wide_data);
> > + ret |= do_one_test (filename);
> > +
> > + return ret;
> > +}
> > diff --git a/libio/wfileops.c b/libio/wfileops.c
> > index 3199861..f123add 100644
> > --- a/libio/wfileops.c
> > +++ b/libio/wfileops.c
> > @@ -713,9 +713,16 @@ do_ftell_wide (_IO_FILE *fp)
> > offset += outstop - out;
> > }
> >
> > - /* _IO_read_end coincides with fp._offset, so the actual file
> > - position is fp._offset - (_IO_read_end - new_write_ptr). */
> > - offset -= fp->_IO_read_end - fp->_IO_write_ptr;
> > + /* We don't trust _IO_read_end to represent the current file offset
> > + when writing in append mode because the value would have to be
> > + shifted to the end of the file during a flush. Use the write base
> > + instead, along with the new offset we got above when we did a seek
> > + to the end of the file. */
> > + if (append_mode)
> > + offset += fp->_IO_write_ptr - fp->_IO_write_base;
> > + /* For all other modes, _IO_read_end represents the file offset. */
> > + else
> > + offset += fp->_IO_write_ptr - fp->_IO_read_end;
> > }
> > }
> >
> > --
> > 1.8.3.1
> >
>
>
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