Re: [PATCH v2 2/2] new: Centralize file type stat-ing logic

[Jani Nikula <jani@nikula.org>]

On Mon,  7 May 2012 18:20:40 -0400, Austin Clements <amdragon@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 symlink-handling logic has been replaced by a simple stat fall-through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).

LGTM.

> ---
>  notmuch-new.c |  103 +++++++++++++++++++++++++++++++++++----------------------
>  test/new      |    2 +-
>  2 files changed, 64 insertions(+), 41 deletions(-)
> 
> diff --git a/notmuch-new.c b/notmuch-new.c
> index cb720cc..8955677 100644
> --- a/notmuch-new.c
> +++ b/notmuch-new.c
> @@ -154,6 +154,48 @@ 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, saved_errno;
> +
> +#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 < ARRAY_SIZE(modes) && modes[entry->d_type])
> +	return modes[entry->d_type];
> +#endif
> +
> +    abspath = talloc_asprintf (NULL, "%s/%s", path, entry->d_name);
> +    if (!abspath) {
> +	errno = ENOMEM;
> +	return -1;
> +    }
> +    err = stat(abspath, &statbuf);
> +    saved_errno = errno;
> +    talloc_free (abspath);
> +    if (err < 0) {
> +	errno = saved_errno;
> +	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 +204,12 @@ 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 +292,7 @@ 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 +359,7 @@ 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 +367,16 @@ 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 lose lots of mail just
> +	     * because a user broke a symlink. */
> +	    fprintf (stderr, "Error reading file %s/%s: %s\n",
> +		     path, entry->d_name, strerror (errno));
> +	    return NOTMUCH_STATUS_FILE_ERROR;
> +	} else if (entry_type != S_IFDIR) {
>  	    continue;
>  	}
>  
> @@ -425,31 +466,13 @@ 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));
> +	    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"
> -- 
> 1.7.10
> 
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