Merge pull request #285 from dscho/readme

[git/mingw/4msysgit.git] / symlinks.c

#include "cache.h"

static int threaded_check_leading_path(struct cache_def *cache, const char *name, int len);
static int threaded_has_dirs_only_path(struct cache_def *cache, const char *name, int len, int prefix_len);

/*
 * Returns the length (on a path component basis) of the longest
 * common prefix match of 'name_a' and 'name_b'.
 */
static int longest_path_match(const char *name_a, int len_a,
                              const char *name_b, int len_b,
                              int *previous_slash)
{
        int max_len, match_len = 0, match_len_prev = 0, i = 0;

        max_len = len_a < len_b ? len_a : len_b;
        while (i < max_len && name_a[i] == name_b[i]) {
                if (name_a[i] == '/') {
                        match_len_prev = match_len;
                        match_len = i;
                }
                i++;
        }
        /*
         * Is 'name_b' a substring of 'name_a', the other way around,
         * or is 'name_a' and 'name_b' the exact same string?
         */
        if (i >= max_len && ((len_a > len_b && name_a[len_b] == '/') ||
                             (len_a < len_b && name_b[len_a] == '/') ||
                             (len_a == len_b))) {
                match_len_prev = match_len;
                match_len = i;
        }
        *previous_slash = match_len_prev;
        return match_len;
}

static struct cache_def default_cache = CACHE_DEF_INIT;

static inline void reset_lstat_cache(struct cache_def *cache)
{
        strbuf_reset(&cache->path);
        cache->flags = 0;
        /*
         * The track_flags and prefix_len_stat_func members is only
         * set by the safeguard rule inside lstat_cache()
         */
}

#define FL_DIR      (1 << 0)
#define FL_NOENT    (1 << 1)
#define FL_SYMLINK  (1 << 2)
#define FL_LSTATERR (1 << 3)
#define FL_ERR      (1 << 4)
#define FL_FULLPATH (1 << 5)

/*
 * Check if name 'name' of length 'len' has a symlink leading
 * component, or if the directory exists and is real, or not.
 *
 * To speed up the check, some information is allowed to be cached.
 * This can be indicated by the 'track_flags' argument, which also can
 * be used to indicate that we should check the full path.
 *
 * The 'prefix_len_stat_func' parameter can be used to set the length
 * of the prefix, where the cache should use the stat() function
 * instead of the lstat() function to test each path component.
 */
static int lstat_cache_matchlen(struct cache_def *cache,
                                const char *name, int len,
                                int *ret_flags, int track_flags,
                                int prefix_len_stat_func)
{
        int match_len, last_slash, last_slash_dir, previous_slash;
        int save_flags, ret;
        struct stat st;

        if (cache->track_flags != track_flags ||
            cache->prefix_len_stat_func != prefix_len_stat_func) {
                /*
                 * As a safeguard rule we clear the cache if the
                 * values of track_flags and/or prefix_len_stat_func
                 * does not match with the last supplied values.
                 */
                reset_lstat_cache(cache);
                cache->track_flags = track_flags;
                cache->prefix_len_stat_func = prefix_len_stat_func;
                match_len = last_slash = 0;
        } else {
                /*
                 * Check to see if we have a match from the cache for
                 * the 2 "excluding" path types.
                 */
                match_len = last_slash =
                        longest_path_match(name, len, cache->path.buf,
                                           cache->path.len, &previous_slash);
                *ret_flags = cache->flags & track_flags & (FL_NOENT|FL_SYMLINK);

                if (!(track_flags & FL_FULLPATH) && match_len == len)
                        match_len = last_slash = previous_slash;

                if (*ret_flags && match_len == cache->path.len)
                        return match_len;
                /*
                 * If we now have match_len > 0, we would know that
                 * the matched part will always be a directory.
                 *
                 * Also, if we are tracking directories and 'name' is
                 * a substring of the cache on a path component basis,
                 * we can return immediately.
                 */
                *ret_flags = track_flags & FL_DIR;
                if (*ret_flags && len == match_len)
                        return match_len;
        }

        /*
         * Okay, no match from the cache so far, so now we have to
         * check the rest of the path components.
         */
        *ret_flags = FL_DIR;
        last_slash_dir = last_slash;
        if (len > cache->path.len)
                strbuf_grow(&cache->path, len - cache->path.len);
        while (match_len < len) {
                do {
                        cache->path.buf[match_len] = name[match_len];
                        match_len++;
                } while (match_len < len && name[match_len] != '/');
                if (match_len >= len && !(track_flags & FL_FULLPATH))
                        break;
                last_slash = match_len;
                cache->path.buf[last_slash] = '\0';

                if (last_slash <= prefix_len_stat_func)
                        ret = stat(cache->path.buf, &st);
                else
                        ret = lstat(cache->path.buf, &st);

                if (ret) {
                        *ret_flags = FL_LSTATERR;
                        if (errno == ENOENT)
                                *ret_flags |= FL_NOENT;
                } else if (S_ISDIR(st.st_mode)) {
                        last_slash_dir = last_slash;
                        continue;
                } else if (S_ISLNK(st.st_mode)) {
                        *ret_flags = FL_SYMLINK;
                } else {
                        *ret_flags = FL_ERR;
                }
                break;
        }

        /*
         * At the end update the cache.  Note that max 3 different
         * path types, FL_NOENT, FL_SYMLINK and FL_DIR, can be cached
         * for the moment!
         */
        save_flags = *ret_flags & track_flags & (FL_NOENT|FL_SYMLINK);
        if (save_flags && last_slash > 0) {
                cache->path.buf[last_slash] = '\0';
                cache->path.len = last_slash;
                cache->flags = save_flags;
        } else if ((track_flags & FL_DIR) && last_slash_dir > 0) {
                /*
                 * We have a separate test for the directory case,
                 * since it could be that we have found a symlink or a
                 * non-existing directory and the track_flags says
                 * that we cannot cache this fact, so the cache would
                 * then have been left empty in this case.
                 *
                 * But if we are allowed to track real directories, we
                 * can still cache the path components before the last
                 * one (the found symlink or non-existing component).
                 */
                cache->path.buf[last_slash_dir] = '\0';
                cache->path.len = last_slash_dir;
                cache->flags = FL_DIR;
        } else {
                reset_lstat_cache(cache);
        }
        return match_len;
}

static int lstat_cache(struct cache_def *cache, const char *name, int len,
                       int track_flags, int prefix_len_stat_func)
{
        int flags;
        (void)lstat_cache_matchlen(cache, name, len, &flags, track_flags,
                        prefix_len_stat_func);
        return flags;
}

#define USE_ONLY_LSTAT  0

/*
 * Return non-zero if path 'name' has a leading symlink component
 */
int threaded_has_symlink_leading_path(struct cache_def *cache, const char *name, int len)
{
        return lstat_cache(cache, name, len, FL_SYMLINK|FL_DIR, USE_ONLY_LSTAT) & FL_SYMLINK;
}

/*
 * Return non-zero if path 'name' has a leading symlink component
 */
int has_symlink_leading_path(const char *name, int len)
{
        return threaded_has_symlink_leading_path(&default_cache, name, len);
}

/*
 * Return zero if path 'name' has a leading symlink component or
 * if some leading path component does not exists.
 *
 * Return -1 if leading path exists and is a directory.
 *
 * Return path length if leading path exists and is neither a
 * directory nor a symlink.
 */
int check_leading_path(const char *name, int len)
{
    return threaded_check_leading_path(&default_cache, name, len);
}

/*
 * Return zero if path 'name' has a leading symlink component or
 * if some leading path component does not exists.
 *
 * Return -1 if leading path exists and is a directory.
 *
 * Return path length if leading path exists and is neither a
 * directory nor a symlink.
 */
static int threaded_check_leading_path(struct cache_def *cache, const char *name, int len)
{
        int flags;
        int match_len = lstat_cache_matchlen(cache, name, len, &flags,
                           FL_SYMLINK|FL_NOENT|FL_DIR, USE_ONLY_LSTAT);
        if (flags & FL_NOENT)
                return 0;
        else if (flags & FL_DIR)
                return -1;
        else
                return match_len;
}

/*
 * Return non-zero if all path components of 'name' exists as a
 * directory.  If prefix_len > 0, we will test with the stat()
 * function instead of the lstat() function for a prefix length of
 * 'prefix_len', thus we then allow for symlinks in the prefix part as
 * long as those points to real existing directories.
 */
int has_dirs_only_path(const char *name, int len, int prefix_len)
{
        return threaded_has_dirs_only_path(&default_cache, name, len, prefix_len);
}

/*
 * Return non-zero if all path components of 'name' exists as a
 * directory.  If prefix_len > 0, we will test with the stat()
 * function instead of the lstat() function for a prefix length of
 * 'prefix_len', thus we then allow for symlinks in the prefix part as
 * long as those points to real existing directories.
 */
static int threaded_has_dirs_only_path(struct cache_def *cache, const char *name, int len, int prefix_len)
{
        return lstat_cache(cache, name, len,
                           FL_DIR|FL_FULLPATH, prefix_len) &
                FL_DIR;
}

static struct strbuf removal = STRBUF_INIT;

static void do_remove_scheduled_dirs(int new_len)
{
        while (removal.len > new_len) {
                removal.buf[removal.len] = '\0';
                if (rmdir(removal.buf))
                        break;
                do {
                        removal.len--;
                } while (removal.len > new_len &&
                         removal.buf[removal.len] != '/');
        }
        removal.len = new_len;
}

void schedule_dir_for_removal(const char *name, int len)
{
        int match_len, last_slash, i, previous_slash;

        match_len = last_slash = i =
                longest_path_match(name, len, removal.buf, removal.len,
                                   &previous_slash);
        /* Find last slash inside 'name' */
        while (i < len) {
                if (name[i] == '/')
                        last_slash = i;
                i++;
        }

        /*
         * If we are about to go down the directory tree, we check if
         * we must first go upwards the tree, such that we then can
         * remove possible empty directories as we go upwards.
         */
        if (match_len < last_slash && match_len < removal.len)
                do_remove_scheduled_dirs(match_len);
        /*
         * If we go deeper down the directory tree, we only need to
         * save the new path components as we go down.
         */
        if (match_len < last_slash)
                strbuf_add(&removal, &name[match_len], last_slash - match_len);
}

void remove_scheduled_dirs(void)
{
        do_remove_scheduled_dirs(0);
}