When using -L with Linux app emulation, there is an issue in init_paths where Qemu will get lost exploring a directory tree with a symlink loop in it. This causes Qemu to hang, and eventually consume all memory in the system.
Qemu's code for pre-exploring the entire directory tree is both error-prone and slow. Instead, this changes uses faccessat, which both avoids the symlink loop (since the entire directory space isn't being explored up front), and likely speeds things up a bit. Partial credit goes to Richard Henderson, as it was only after staring at his patch [1] that I wrote mine. [1] https://patchwork.kernel.org/patch/9512083/ Signed-off-by: Evan Green <evgr...@chromium.org> --- Since the path() function returns a final path, I used a thread-local global to contain the glued-together path. From my examination of the callers of path(), this is sufficient. The thread-localness of it may not actually be necessary, but it seemed safer. I can remove the __thread attribute if desired. --- util/path.c | 159 ++++++++---------------------------------------------------- 1 file changed, 21 insertions(+), 138 deletions(-) diff --git a/util/path.c b/util/path.c index 7f9fc272fb..b9a0e8ef47 100644 --- a/util/path.c +++ b/util/path.c @@ -4,133 +4,13 @@ The assumption is that this area does not change. */ #include "qemu/osdep.h" -#include <sys/param.h> -#include <dirent.h> +#include <limits.h> #include "qemu/cutils.h" #include "qemu/path.h" -struct pathelem -{ - /* Name of this, eg. lib */ - char *name; - /* Full path name, eg. /usr/gnemul/x86-linux/lib. */ - char *pathname; - struct pathelem *parent; - /* Children */ - unsigned int num_entries; - struct pathelem *entries[0]; -}; - -static struct pathelem *base; - -/* First N chars of S1 match S2, and S2 is N chars long. */ -static int strneq(const char *s1, unsigned int n, const char *s2) -{ - unsigned int i; - - for (i = 0; i < n; i++) - if (s1[i] != s2[i]) - return 0; - return s2[i] == 0; -} - -static struct pathelem *add_entry(struct pathelem *root, const char *name, - unsigned type); - -static struct pathelem *new_entry(const char *root, - struct pathelem *parent, - const char *name) -{ - struct pathelem *new = g_malloc(sizeof(*new)); - new->name = g_strdup(name); - new->pathname = g_strdup_printf("%s/%s", root, name); - new->num_entries = 0; - return new; -} - -#define streq(a,b) (strcmp((a), (b)) == 0) - -/* Not all systems provide this feature */ -#if defined(DT_DIR) && defined(DT_UNKNOWN) && defined(DT_LNK) -# define dirent_type(dirent) ((dirent)->d_type) -# define is_dir_maybe(type) \ - ((type) == DT_DIR || (type) == DT_UNKNOWN || (type) == DT_LNK) -#else -# define dirent_type(dirent) (1) -# define is_dir_maybe(type) (type) -#endif - -static struct pathelem *add_dir_maybe(struct pathelem *path) -{ - DIR *dir; - - if ((dir = opendir(path->pathname)) != NULL) { - struct dirent *dirent; - - while ((dirent = readdir(dir)) != NULL) { - if (!streq(dirent->d_name,".") && !streq(dirent->d_name,"..")){ - path = add_entry(path, dirent->d_name, dirent_type(dirent)); - } - } - closedir(dir); - } - return path; -} - -static struct pathelem *add_entry(struct pathelem *root, const char *name, - unsigned type) -{ - struct pathelem **e; - - root->num_entries++; - - root = g_realloc(root, sizeof(*root) - + sizeof(root->entries[0])*root->num_entries); - e = &root->entries[root->num_entries-1]; - - *e = new_entry(root->pathname, root, name); - if (is_dir_maybe(type)) { - *e = add_dir_maybe(*e); - } - - return root; -} - -/* This needs to be done after tree is stabilized (ie. no more reallocs!). */ -static void set_parents(struct pathelem *child, struct pathelem *parent) -{ - unsigned int i; - - child->parent = parent; - for (i = 0; i < child->num_entries; i++) - set_parents(child->entries[i], child); -} - -/* FIXME: Doesn't handle DIR/.. where DIR is not in emulated dir. */ -static const char * -follow_path(const struct pathelem *cursor, const char *name) -{ - unsigned int i, namelen; - - name += strspn(name, "/"); - namelen = strcspn(name, "/"); - - if (namelen == 0) - return cursor->pathname; - - if (strneq(name, namelen, "..")) - return follow_path(cursor->parent, name + namelen); - - if (strneq(name, namelen, ".")) - return follow_path(cursor, name + namelen); - - for (i = 0; i < cursor->num_entries; i++) - if (strneq(name, namelen, cursor->entries[i]->name)) - return follow_path(cursor->entries[i], name + namelen); - - /* Not found */ - return NULL; -} +static const char *pathprefix; +int pathprefixfd = -1; +__thread char gluedpath[PATH_MAX]; void init_paths(const char *prefix) { @@ -150,28 +30,31 @@ void init_paths(const char *prefix) pstrcat(pref_buf, pref_buf_len, "/"); pstrcat(pref_buf, pref_buf_len, prefix); free(cwd); - } else - pstrcpy(pref_buf, sizeof(pref_buf), prefix + 1); - - base = new_entry("", NULL, pref_buf); - base = add_dir_maybe(base); - if (base->num_entries == 0) { - g_free(base->pathname); - g_free(base->name); - g_free(base); - base = NULL; - } else { - set_parents(base, base); + prefix = strdup(pref_buf); + if (!prefix) { + abort(); + } } + + pathprefix = prefix; + pathprefixfd = open(pathprefix, O_RDONLY | O_DIRECTORY | O_CLOEXEC); } /* Look for path in emulation dir, otherwise return name. */ const char *path(const char *name) { + const char *relname; /* Only do absolute paths: quick and dirty, but should mostly be OK. Could do relative by tracking cwd. */ - if (!base || !name || name[0] != '/') + if ((pathprefixfd < 0) || !name || name[0] != '/') { return name; + } + + relname = name + strspn(name, "/"); + if (faccessat(pathprefixfd, relname, R_OK, AT_EACCESS) == 0) { + snprintf(gluedpath, sizeof(gluedpath), "%s%s", pathprefix, name); + return gluedpath; + } - return follow_path(base, name) ?: name; + return name; } -- 2.13.5
