optional /etc/localtime support

This patch teaches uclibc to use /etc/localtime.
This is possible since recent TZif2 file format contains
TZ-like ASCII string at the end.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

diff --git a/extra/Configs/Config.in b/extra/Configs/Config.in
index 21c14ac..6803659 100644 (file)
--- a/extra/Configs/Config.in
+++ b/extra/Configs/Config.in
@@ -848,6 +848,17 @@ config UCLIBC_TZ_FILE_PATH
 
          Most people will use the default of '/etc/TZ'.
 
+config UCLIBC_FALLBACK_TO_ETC_LOCALTIME
+       bool "Use /etc/localtime as a fallback"
+       depends on UCLIBC_HAS_TZ_FILE
+       default y
+       help
+         Answer Y to try to use /etc/localtime file.
+         On glibc systems this file (if it is in TZif2 format)
+         contains timezone string at the end.
+
+         Most people will answer Y.
+
 endmenu
 
 menu "Advanced Library Settings"

diff --git a/libc/misc/time/time.c b/libc/misc/time/time.c
index dfa8c0d..f80104e 100644 (file)
--- a/libc/misc/time/time.c
+++ b/libc/misc/time/time.c
@@ -1804,12 +1804,12 @@ static smallint TZ_file_read;           /* Let BSS initialization set this to 0. */
 
 static char *read_TZ_file(char *buf)
 {
+       int r;
        int fd;
        char *p = NULL;
 
        fd = open(__UCLIBC_TZ_FILE_PATH__, O_RDONLY);
        if (fd >= 0) {
-               ssize_t r;
 #if 0
                /* TZ are small *files*. On files, short reads
                 * only occur on EOF (unlike, say, pipes).
@@ -1829,13 +1829,12 @@ static char *read_TZ_file(char *buf)
                        todo -= r;
                } while (todo);
 #else
-               /* Shorter, and does one less read syscall */
+               /* Shorter, and does one fewer read syscall */
                r = read(fd, buf, TZ_BUFLEN);
                if (r < 0)
                        goto ERROR;
                p = buf + r;
 #endif
-
                if ((p > buf) && (p[-1] == '\n')) { /* Must end with newline */
                        p[-1] = 0;
                        p = buf;
@@ -1848,6 +1847,45 @@ ERROR:
                }
                close(fd);
        }
+#ifdef __UCLIBC_FALLBACK_TO_ETC_LOCALTIME__
+       else {
+               fd = open("/etc/localtime", O_RDONLY);
+               if (fd >= 0) {
+                       r = read(fd, buf, TZ_BUFLEN);
+                       if (r != TZ_BUFLEN
+                        || strncmp(buf, "TZif", 4) != 0
+                        || (unsigned char)buf[4] < 2
+                        || lseek(fd, -TZ_BUFLEN, SEEK_END) < 0
+                       ) {
+                               goto ERROR;
+                       }
+                       /* tzfile.h from tzcode database says about TZif2+ files:
+                       **
+                       ** If tzh_version is '2' or greater, the above is followed by a second instance
+                       ** of tzhead and a second instance of the data in which each coded transition
+                       ** time uses 8 rather than 4 chars,
+                       ** then a POSIX-TZ-environment-variable-style string for use in handling
+                       ** instants after the last transition time stored in the file
+                       ** (with nothing between the newlines if there is no POSIX representation for
+                       ** such instants).
+                       */
+                       r = read(fd, buf, TZ_BUFLEN);
+                       if (r <= 0 || buf[--r] != '\n')
+                               goto ERROR;
+                       buf[r] = 0;
+                       while (r != 0) {
+                               if (buf[--r] == '\n') {
+                                       p = buf + r + 1;
+#ifndef __UCLIBC_HAS_TZ_FILE_READ_MANY__
+                                       TZ_file_read = 1;
+#endif
+                                       break;
+                               }
+                       } /* else ('\n' not found): p remains NULL */
+                       close(fd);
+               }
+       }
+#endif /* __UCLIBC_FALLBACK_TO_ETC_LOCALTIME__ */
        return p;
 }