[Bug stdio/17647] New: ftell after ftruncate reports incorrect offset

[Bug stdio/17647] New: ftell after ftruncate reports incorrect offset

[siddhesh at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=17647

            Bug ID: 17647
           Summary: ftell after ftruncate reports incorrect offset
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: stdio
          Assignee: siddhesh at redhat dot com
          Reporter: siddhesh at redhat dot com

Currently we seek to end of file if there are unflushed writes or the
stream is in write mode, to get the current offset for writing in
append mode, which is the end of file.  The latter case (i.e. stream
is in write mode, but no unflushed writes) is unnecessary since it
will only happen when the stream has just been flushed, in which case
the recorded offset ought to be reliable.

Removing that case lets ftell give the correct offset when it follows
an ftruncate.  The latter truncates the file, but does not change the
file position, due to which it is permissible to call ftell without an
intervening fseek call.

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[Bug stdio/17647] ftell after ftruncate reports incorrect offset

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=17647

--- Comment #1 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
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The branch, master has been updated
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https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=24b9788285effddba3d52f174d483583cf820d19

commit 24b9788285effddba3d52f174d483583cf820d19
Author: Siddhesh Poyarekar <siddhesh@redhat.com>
Date:   Thu Dec 4 08:45:55 2014 +0530

    Fix up function definition style

    Don't use K&R style for function definitions.

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=fe8b4d98e9ac371238388469cb74011cb2120343

commit fe8b4d98e9ac371238388469cb74011cb2120343
Author: Siddhesh Poyarekar <siddhesh@redhat.com>
Date:   Thu Dec 4 08:13:28 2014 +0530

    Reset cached offset when reading to end of stream (BZ #17653)

    POSIX allows applications to switch file handles when a read results
    in an end of file.  Unset the cached offset at this point so that it
    is queried again.

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=61b4f792e03facb456036b3f631d58d4f53b8075

commit 61b4f792e03facb456036b3f631d58d4f53b8075
Author: Siddhesh Poyarekar <siddhesh@redhat.com>
Date:   Thu Dec 4 08:11:07 2014 +0530

    tst-ftell-active-handler: Open file with O_TRUNC for w modes

    The test case fails to truncate the file when a file is intended to be
    opened in w or w+ mode.  Add O_TRUNC to fix this.  The test still
    succeeds with this change.

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=be349d7042de84c3c5157a5c1fbcad580aed33e1

commit be349d7042de84c3c5157a5c1fbcad580aed33e1
Author: Siddhesh Poyarekar <siddhesh@redhat.com>
Date:   Thu Dec 4 08:08:37 2014 +0530

    ftell: seek to end only when there are unflushed bytes (BZ #17647)

    Currently we seek to end of file if there are unflushed writes or the
    stream is in write mode, to get the current offset for writing in
    append mode, which is the end of file.  The latter case (i.e. stream
    is in write mode, but no unflushed writes) is unnecessary since it
    will only happen when the stream has just been flushed, in which case
    the recorded offset ought to be reliable.

    Removing that case lets ftell give the correct offset when it follows
    an ftruncate.  The latter truncates the file, but does not change the
    file position, due to which it is permissible to call ftell without an
    intervening fseek call.

    Tested on x86_64 to verify that the added test case fails without the
    patch and succeeds with it, and that there are no additional
    regressions due to it.

        [BZ #17647]
        * libio/fileops.c (do_ftell): Seek only when there are
        unflushed writes.
        * libio/wfileops.c (do_ftell_wide): Likewise.
        * libio/tst-ftell-active-handler.c (do_ftruncate_test): New
        test case.
        (do_one_test): Call it.

-----------------------------------------------------------------------

Summary of changes:
 ChangeLog                        |   30 ++++++++
 NEWS                             |    2 +-
 libio/fileops.c                  |  134 +++++++++------------------------
 libio/iofopen.c                  |   12 +--
 libio/tst-ftell-active-handler.c |  152 +++++++++++++++++++++++++++++++++++---
 libio/wfileops.c                 |   40 ++++-------
 6 files changed, 225 insertions(+), 145 deletions(-)

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[Bug stdio/17647] ftell after ftruncate reports incorrect offset

[siddhesh at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=17647

Siddhesh Poyarekar <siddhesh at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED

--- Comment #2 from Siddhesh Poyarekar <siddhesh at redhat dot com> ---
Fixed in master.

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