file_utils: introduce read_file_at()

Cc: stable-4.0
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

diff --git a/src/lxc/cgroups/cgfsng.c b/src/lxc/cgroups/cgfsng.c
index 138d01ee2eb194692df56199bf539ce1ace489dc..3dffcd944b8e47bb25f2c09136d6b720dffd020f 100644 (file)
--- a/src/lxc/cgroups/cgfsng.c
+++ b/src/lxc/cgroups/cgfsng.c
@@ -176,45 +176,6 @@ static struct hierarchy *get_hierarchy(struct cgroup_ops *ops, const char *contr
        return ret_set_errno(NULL, ENOENT);
 }
 
-#define BATCH_SIZE 50
-static void batch_realloc(char **mem, size_t oldlen, size_t newlen)
-{
-       int newbatches = (newlen / BATCH_SIZE) + 1;
-       int oldbatches = (oldlen / BATCH_SIZE) + 1;
-
-       if (!*mem || newbatches > oldbatches)
-               *mem = must_realloc(*mem, newbatches * BATCH_SIZE);
-}
-
-static void append_line(char **dest, size_t oldlen, char *new, size_t newlen)
-{
-       size_t full = oldlen + newlen;
-
-       batch_realloc(dest, oldlen, full + 1);
-
-       memcpy(*dest + oldlen, new, newlen + 1);
-}
-
-/* Slurp in a whole file */
-static char *read_file(const char *fnam)
-{
-       __do_free char *buf = NULL, *line = NULL;
-       __do_fclose FILE *f = NULL;
-       size_t len = 0, fulllen = 0;
-       int linelen;
-
-       f = fopen(fnam, "re");
-       if (!f)
-               return NULL;
-
-       while ((linelen = getline(&line, &len, f)) != -1) {
-               append_line(&buf, fulllen, line, linelen);
-               fulllen += linelen;
-       }
-
-       return move_ptr(buf);
-}
-
 /* Taken over modified from the kernel sources. */
 #define NBITS 32 /* bits in uint32_t */
 #define DIV_ROUND_UP(n, d) (((n) + (d)-1) / (d))
@@ -350,7 +311,7 @@ static bool cg_legacy_filter_and_set_cpus(const char *parent_cgroup,
        bool flipped_bit = false;
 
        fpath = must_make_path(parent_cgroup, "cpuset.cpus", NULL);
-       posscpus = read_file(fpath);
+       posscpus = read_file_at(-EBADF, fpath);
        if (!posscpus)
                return log_error_errno(false, errno, "Failed to read file \"%s\"", fpath);
 
@@ -360,7 +321,7 @@ static bool cg_legacy_filter_and_set_cpus(const char *parent_cgroup,
                return false;
 
        if (file_exists(__ISOL_CPUS)) {
-               isolcpus = read_file(__ISOL_CPUS);
+               isolcpus = read_file_at(-EBADF, __ISOL_CPUS);
                if (!isolcpus)
                        return log_error_errno(false, errno, "Failed to read file \"%s\"", __ISOL_CPUS);
 
@@ -379,7 +340,7 @@ static bool cg_legacy_filter_and_set_cpus(const char *parent_cgroup,
        }
 
        if (file_exists(__OFFLINE_CPUS)) {
-               offlinecpus = read_file(__OFFLINE_CPUS);
+               offlinecpus = read_file_at(-EBADF, __OFFLINE_CPUS);
                if (!offlinecpus)
                        return log_error_errno(false, errno, "Failed to read file \"%s\"", __OFFLINE_CPUS);
 
@@ -691,14 +652,14 @@ static char **cg_unified_make_empty_controller(void)
        return move_ptr(aret);
 }
 
-static char **cg_unified_get_controllers(const char *file)
+static char **cg_unified_get_controllers(int dfd, const char *file)
 {
        __do_free char *buf = NULL;
        __do_free_string_list char **aret = NULL;
        char *sep = " \t\n";
        char *tok;
 
-       buf = read_file(file);
+       buf = read_file_at(dfd, file);
        if (!buf)
                return NULL;
 
@@ -3148,7 +3109,7 @@ static void cg_unified_delegate(char ***delegate)
        char *token;
        int idx;
 
-       buf = read_file("/sys/kernel/cgroup/delegate");
+       buf = read_file_at(-EBADF, "/sys/kernel/cgroup/delegate");
        if (!buf) {
                for (char **p = standard; p && *p; p++) {
                        idx = append_null_to_list((void ***)delegate);
@@ -3186,9 +3147,9 @@ static int cg_hybrid_init(struct cgroup_ops *ops, bool relative, bool unprivileg
         * cgroups as our base in that case.
         */
        if (!relative && (geteuid() == 0))
-               basecginfo = read_file("/proc/1/cgroup");
+               basecginfo = read_file_at(-EBADF, "/proc/1/cgroup");
        else
-               basecginfo = read_file("/proc/self/cgroup");
+               basecginfo = read_file_at(-EBADF, "/proc/self/cgroup");
        if (!basecginfo)
                return ret_set_errno(-1, ENOMEM);
 
@@ -3272,7 +3233,7 @@ static int cg_hybrid_init(struct cgroup_ops *ops, bool relative, bool unprivileg
                                                        "cgroup.controllers",
                                                        NULL);
 
-                       controller_list = cg_unified_get_controllers(cgv2_ctrl_path);
+                       controller_list = cg_unified_get_controllers(-EBADF, cgv2_ctrl_path);
                        free(cgv2_ctrl_path);
                        if (!controller_list) {
                                controller_list = cg_unified_make_empty_controller();
@@ -3315,9 +3276,9 @@ static char *cg_unified_get_current_cgroup(bool relative)
        char *base_cgroup;
 
        if (!relative && (geteuid() == 0))
-               basecginfo = read_file("/proc/1/cgroup");
+               basecginfo = read_file_at(-EBADF, "/proc/1/cgroup");
        else
-               basecginfo = read_file("/proc/self/cgroup");
+               basecginfo = read_file_at(-EBADF, "/proc/self/cgroup");
        if (!basecginfo)
                return NULL;
 

diff --git a/src/lxc/file_utils.c b/src/lxc/file_utils.c
index a8d9aaf3046c5587ca55a4e3c7f68504c094bc23..02856153ac15d161f627e72aacc2c099c7ebd12e 100644 (file)
--- a/src/lxc/file_utils.c
+++ b/src/lxc/file_utils.c
@@ -592,3 +592,49 @@ int fd_make_nonblocking(int fd)
        flags &= ~O_NONBLOCK;
        return fcntl(fd, F_SETFL, flags);
 }
+
+#define BATCH_SIZE 50
+static void batch_realloc(char **mem, size_t oldlen, size_t newlen)
+{
+       int newbatches = (newlen / BATCH_SIZE) + 1;
+       int oldbatches = (oldlen / BATCH_SIZE) + 1;
+
+       if (!*mem || newbatches > oldbatches)
+               *mem = must_realloc(*mem, newbatches * BATCH_SIZE);
+}
+
+static void append_line(char **dest, size_t oldlen, char *new, size_t newlen)
+{
+       size_t full = oldlen + newlen;
+
+       batch_realloc(dest, oldlen, full + 1);
+
+       memcpy(*dest + oldlen, new, newlen + 1);
+}
+
+/* Slurp in a whole file */
+char *read_file_at(int dfd, const char *fnam)
+{
+       __do_close int fd = -EBADF;
+       __do_free char *buf = NULL, *line = NULL;
+       __do_fclose FILE *f = NULL;
+       size_t len = 0, fulllen = 0;
+       int linelen;
+
+       fd = openat(dfd, fnam, O_NOCTTY | O_CLOEXEC | O_NOFOLLOW | O_RDONLY);
+       if (fd < 0)
+               return NULL;
+
+       f = fdopen(fd, "re");
+       if (!f)
+               return NULL;
+       /* Transfer ownership to fdopen(). */
+       move_fd(fd);
+
+       while ((linelen = getline(&line, &len, f)) != -1) {
+               append_line(&buf, fulllen, line, linelen);
+               fulllen += linelen;
+       }
+
+       return move_ptr(buf);
+}

diff --git a/src/lxc/file_utils.h b/src/lxc/file_utils.h
index 11acdb3a7b027b75fb5a89b72fec49bdcbdd2722..7652b09ff405b28dbe6b77e15618783409691631 100644 (file)
--- a/src/lxc/file_utils.h
+++ b/src/lxc/file_utils.h
@@ -81,5 +81,6 @@ __hidden extern bool exists_dir_at(int dir_fd, const char *path);
 __hidden extern bool exists_file_at(int dir_fd, const char *path);
 __hidden extern int open_beneath(int dir_fd, const char *path, unsigned int flags);
 __hidden int fd_make_nonblocking(int fd);
+__hidden extern char *read_file_at(int dfd, const char *fnam);
 
 #endif /* __LXC_FILE_UTILS_H */