[PATCH 2/2] new: Centralize file type stat-ing logic

Austin Clements amdragon at MIT.EDU
Mon May 7 15:18:33 PDT 2012


Quoth Jani Nikula on May 08 at 12:08 am:
>    On May 7, 2012 9:10 PM, "Austin Clements" <[1]amdragon at mit.edu> wrote:
>    >
>    > This moves our logic to get a file's type into one function.  This has
>    > several benefits: we can support OSes and file systems that do not
>    > provide dirent.d_type or always return DT_UNKNOWN, complex
>    > symlink-handling logic has been replaced by a simple stat fall-through
>    > in one place, and the error message for un-stat-able file is more
>    > accurate (previously, the error always mentioned directories, even
>    > though a broken symlink is not a directory).
> 
>    Please find some quick drive-by-review below.

Thanks for the review!  New version on its way...

>    J.
> 
>    > ---
>    >  notmuch-new.c |   99
>    ++++++++++++++++++++++++++++++++++-----------------------
>    >  test/new      |    2 +-
>    >  2 files changed, 60 insertions(+), 41 deletions(-)
>    >
>    > diff --git a/notmuch-new.c b/notmuch-new.c
>    > index cb720cc..cf2580e 100644
>    > --- a/notmuch-new.c
>    > +++ b/notmuch-new.c
>    > @@ -154,6 +154,44 @@ dirent_sort_strcmp_name (const struct dirent **a,
>    const struct dirent **b)
>    >     return strcmp ((*a)->d_name, (*b)->d_name);
>    >  }
>    >
>    > +/* Return the type of a directory entry relative to path as a stat(2)
>    > + * mode.  Like stat, this follows symlinks.  Returns -1 and sets errno
>    > + * if the file's type cannot be determined (which includes dangling
>    > + * symlinks).
>    > + */
>    > +static int
>    > +dirent_type (const char *path, const struct dirent *entry)
>    > +{
>    > +    struct stat statbuf;
>    > +    char *abspath;
>    > +    int err;
>    > +
>    > +#ifdef _DIRENT_HAVE_D_TYPE
>    > +    /* Mapping from d_type to stat mode_t.  We omit DT_LNK so that
>    > +     * we'll fall through to stat and get the real file type. */
>    > +    static const mode_t modes[] = {
>    > +       [DT_BLK]  = S_IFBLK,
>    > +       [DT_CHR]  = S_IFCHR,
>    > +       [DT_DIR]  = S_IFDIR,
>    > +       [DT_FIFO] = S_IFIFO,
>    > +       [DT_REG]  = S_IFREG,
>    > +       [DT_SOCK] = S_IFSOCK
>    > +    };
>    > +    if (entry->d_type < sizeof(modes)/sizeof(modes[0]) &&
> 
>    ARRAY_SIZE()

Huh.  I went looking for that.  I wonder how I missed it.

>    > +       modes[entry->d_type])
>    > +       return modes[entry->d_type];
>    > +#endif
>    > +
>    > +    abspath = talloc_asprintf (NULL, "%s/%s", path, entry->d_name);
>    > +    if (!abspath)
>    > +       return -1;
> 
>    Does talloc set errno in this case? I suspect not.
> 
>    > +    err = stat(abspath, &statbuf);
>    > +    talloc_free (abspath);
> 
>    This likely breaks your promise about errno. You can't trust talloc_free()
>    not calling some function that sets errno.

Setting errno was a late and apparently not well thought-out addition.
The new patch should set it on all of the error paths and save it
around things that may modify it.

>    > +    if (err < 0)
>    > +       return -1;
>    > +    return statbuf.st_mode & S_IFMT;
>    > +}
>    > +
>    >  /* Test if the directory looks like a Maildir directory.
>    >  *
>    >  * Search through the array of directory entries to see if we can find
>    all
>    > @@ -162,12 +200,12 @@ dirent_sort_strcmp_name (const struct dirent **a,
>    const struct dirent **b)
>    >  * Return 1 if the directory looks like a Maildir and 0 otherwise.
>    >  */
>    >  static int
>    > -_entries_resemble_maildir (struct dirent **entries, int count)
>    > +_entries_resemble_maildir (const char *path, struct dirent **entries,
>    int count)
>    >  {
>    >     int i, found = 0;
>    >
>    >     for (i = 0; i < count; i++) {
>    > -       if (entries[i]->d_type != DT_DIR && entries[i]->d_type !=
>    DT_UNKNOWN)
>    > +       if (dirent_type (path, entries[i]) != S_IFDIR)
>    >            continue;
>    >
>    >        if (strcmp(entries[i]->d_name, "new") == 0 ||
>    > @@ -250,7 +288,7 @@ add_files_recursive (notmuch_database_t *notmuch,
>    >     notmuch_status_t status, ret = NOTMUCH_STATUS_SUCCESS;
>    >     notmuch_message_t *message = NULL;
>    >     struct dirent **fs_entries = NULL;
>    > -    int i, num_fs_entries;
>    > +    int i, num_fs_entries, entry_type;
>    >     notmuch_directory_t *directory;
>    >     notmuch_filenames_t *db_files = NULL;
>    >     notmuch_filenames_t *db_subdirs = NULL;
>    > @@ -317,7 +355,7 @@ add_files_recursive (notmuch_database_t *notmuch,
>    >     }
>    >
>    >     /* Pass 1: Recurse into all sub-directories. */
>    > -    is_maildir = _entries_resemble_maildir (fs_entries,
>    num_fs_entries);
>    > +    is_maildir = _entries_resemble_maildir (path, fs_entries,
>    num_fs_entries);
>    >
>    >     for (i = 0; i < num_fs_entries; i++) {
>    >        if (interrupted)
>    > @@ -325,17 +363,16 @@ add_files_recursive (notmuch_database_t *notmuch,
>    >
>    >        entry = fs_entries[i];
>    >
>    > -       /* We only want to descend into directories.
>    > -        * But symlinks can be to directories too, of course.
>    > -        *
>    > -        * And if the filesystem doesn't tell us the file type in the
>    > -        * scandir results, then it might be a directory (and if not,
>    > -        * then we'll stat and return immediately in the next level of
>    > -        * recursion). */
>    > -       if (entry->d_type != DT_DIR &&
>    > -           entry->d_type != DT_LNK &&
>    > -           entry->d_type != DT_UNKNOWN)
>    > -       {
>    > +       /* We only want to descend into directories (and symlinks to
>    > +        * directories). */
>    > +       entry_type = dirent_type (path, entry);
>    > +       if (entry_type == -1) {
>    > +           /* Be pessimistic, e.g. so we don't loose lots of mail
> 
>    s/loose/lose/ ?

Oops.

>    > +            * just because a user broke a symlink. */
>    > +           fprintf (stderr, "Error reading file %s/%s: %s\n",
>    > +                    path, entry->d_name, strerror (errno));
> 
>    You can't trust errno here, as explained above.

Fixed above.

>    > +           return NOTMUCH_STATUS_FILE_ERROR;
>    > +       } else if (entry_type != S_IFDIR) {
>    >            continue;
>    >        }
>    >
>    > @@ -425,31 +462,13 @@ add_files_recursive (notmuch_database_t *notmuch,
>    >            notmuch_filenames_move_to_next (db_subdirs);
>    >        }
>    >
>    > -       /* If we're looking at a symlink, we only want to add it if it
>    > -        * links to a regular file, (and not to a directory, say).
>    > -        *
>    > -        * Similarly, if the file is of unknown type (due to filesystem
>    > -        * limitations), then we also need to look closer.
>    > -        *
>    > -        * In either case, a stat does the trick.
>    > -        */
>    > -       if (entry->d_type == DT_LNK || entry->d_type == DT_UNKNOWN) {
>    > -           int err;
>    > -
>    > -           next = talloc_asprintf (notmuch, "%s/%s", path,
>    entry->d_name);
>    > -           err = stat (next, &st);
>    > -           talloc_free (next);
>    > -           next = NULL;
>    > -
>    > -           /* Don't emit an error for a link pointing nowhere, since
>    > -            * the directory-traversal pass will have already done
>    > -            * that. */
>    > -           if (err)
>    > -               continue;
>    > -
>    > -           if (! S_ISREG (st.st_mode))
>    > -               continue;
>    > -       } else if (entry->d_type != DT_REG) {
>    > +       /* Only add regular files (and symlinks to regular files). */
>    > +       entry_type = dirent_type (path, entry);
>    > +       if (entry_type == -1) {
>    > +           fprintf (stderr, "Error reading file %s/%s: %s\n",
>    > +                    path, entry->d_name, strerror (errno));
> 
>    Ditto.
> 
>    > +           return NOTMUCH_STATUS_FILE_ERROR;
>    > +       } else if (entry_type != S_IFREG) {
>    >            continue;
>    >        }
>    >
>    > diff --git a/test/new b/test/new
>    > index 26253db..e3900f5 100755
>    > --- a/test/new
>    > +++ b/test/new
>    > @@ -140,7 +140,7 @@ test_begin_subtest "Broken symlink aborts"
>    >  ln -s does-not-exist "${MAIL_DIR}/broken"
>    >  output=$(NOTMUCH_NEW 2>&1)
>    >  test_expect_equal "$output" \
>    > -"Error reading directory /run/shm/nm/tmp.new/mail/broken: No such file
>    or directory
>    > +"Error reading file /run/shm/nm/tmp.new/mail/broken: No such file or
>    directory
>    >  Note: A fatal error was encountered: Something went wrong trying to
>    read or write a file
>    >  No new mail."
>    >  rm "${MAIL_DIR}/broken"
>    >
>    > _______________________________________________
>    > notmuch mailing list
>    > [2]notmuch at notmuchmail.org
>    > [3]http://notmuchmail.org/mailman/listinfo/notmuch


More information about the notmuch mailing list