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

Jani Nikula jani at nikula.org
Mon May 7 14:08:35 PDT 2012


On May 7, 2012 9:10 PM, "Austin Clements" <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 symlink-handling logic has been replaced by a simple stat fall-through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.

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()

> +       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.

> +    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/ ?

> +            * 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.

> +           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"
> --
> 1.7.10
>
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