Rewrite filesystem code (WIP)

This patch redoes the filesystem code from the FAT driver up to the
clipboard code in onplay.c.

Not every aspect of this is finished therefore it is still "WIP". I
don't wish to do too much at once (haha!). What is left to do is get
dircache back in the sim and find an implementation for the dircache
indicies in the tagcache and playlist code or do something else that
has the same benefit. Leaving these out for now does not make anything
unusable. All the basics are done.

Phone app code should probably get vetted (and app path handling
just plain rewritten as environment expansions); the SDL app and
Android run well.

Main things addressed:
1) Thread safety: There is none right now in the trunk code. Most of
what currently works is luck when multiple threads are involved or
multiple descriptors to the same file are open.

2) POSIX compliance: Many of the functions behave nothing like their
counterparts on a host system. This leads to inconsistent code or very
different behavior from native to hosted. One huge offender was
rename(). Going point by point would fill a book.

3) Actual running RAM usage: Many targets will use less RAM and less
stack space (some more RAM because I upped the number of cache buffers
for large memory). There's very little memory lying fallow in rarely-used
areas (see 'Key core changes' below). Also, all targets may open the same
number of directory streams whereas before those with less than 8MB RAM
were limited to 8, not 12 implying those targets will save slightly
less.

4) Performance: The test_disk plugin shows markedly improved performance,
particularly in the area of (uncached) directory scanning, due partly to
more optimal directory reading and to a better sector cache algorithm.
Uncached times tend to be better while there is a bit of a slowdown in
dircache due to it being a bit heavier of an implementation. It's not
noticeable by a human as far as I can say.

Key core changes:
1) Files and directories share core code and data structures.

2) The filesystem code knows which descriptors refer to same file.
This ensures that changes from one stream are appropriately reflected
in every open descriptor for that file (fileobj_mgr.c).

3) File and directory cache buffers are borrowed from the main sector
cache. This means that when they are not in use by a file, they are not
wasted, but used for the cache. Most of the time, only a few of them
are needed. It also means that adding more file and directory handles
is less expensive. All one must do in ensure a large enough cache to
borrow from.

4) Relative path components are supported and the namespace is unified.
It does not support full relative paths to an implied current directory;
what is does support is use of "." and "..". Adding the former would
not be very difficult. The namespace is unified in the sense that
volumes may be specified several times along with relative parts, e.g.:
"/<0>/foo/../../<1>/bar" :<=> "/<1>/bar".

5) Stack usage is down due to sharing of data, static allocation and
less duplication of strings on the stack. This requires more
serialization than I would like but since the number of threads is
limited to a low number, the tradoff in favor of the stack seems
reasonable.

6) Separates and heirarchicalizes (sic) the SIM and APP filesystem
code. SIM path and volume handling is just like the target. Some
aspects of the APP file code get more straightforward (e.g. no path
hashing is needed).

Dircache:
Deserves its own section. Dircache is new but pays homage to the old.
The old one was not compatible and so it, since it got redone, does
all the stuff it always should have done such as:

1) It may be update and used at any time during the build process.
No longer has one to wait for it to finish building to do basic file
management (create, remove, rename, etc.).

2) It does not need to be either fully scanned or completely disabled;
it can be incomplete (i.e. overfilled, missing paths), still be
of benefit and be correct.

3) Handles mounting and dismounting of individual volumes which means
a full rebuild is not needed just because you pop a new SD card in the
slot. Now, because it reuses its freed entry data, may rebuild only
that volume.

4) Much more fundamental to the file code. When it is built, it is
the keeper of the master file list whether enabled or not ("disabled"
is just a state of the cache). Its must always to ready to be started
and bind all streams opened prior to being enabled.

5) Maintains any short filenames in OEM format which means that it does
not need to be rebuilt when changing the default codepage.

Miscellaneous Compatibility:
1) Update any other code that would otherwise not work such as the
hotswap mounting code in various card drivers.

2) File management: Clipboard needed updating because of the behavioral
changes. Still needs a little more work on some finer points.

3) Remove now-obsolete functionality such as the mutex's "no preempt"
flag (which was only for the prior FAT driver).

4) struct dirinfo uses time_t rather than raw FAT directory entry
time fields. I plan to follow up on genericizing everything there
(i.e. no FAT attributes).

5) unicode.c needed some redoing so that the file code does not try
try to load codepages during a scan, which is actually a problem with
the current code. The default codepage, if any is required, is now
kept in RAM separarately (bufalloced) from codepages specified to
iso_decode() (which must not be bufalloced because the conversion
may be done by playback threads).

Brings with it some additional reusable core code:
1) Revised file functions: Reusable code that does things such as
safe path concatenation and parsing without buffer limitations or
data duplication. Variants that copy or alter the input path may be
based off these.

To do:
1) Put dircache functionality back in the sim. Treating it internally
as a different kind of file system seems the best approach at this
time.

2) Restore use of dircache indexes in the playlist and database or
something effectively the same. Since the cache doesn't have to be
complete in order to be used, not getting a hit on the cache doesn't
unambiguously say if the path exists or not.

Change-Id: Ia30f3082a136253e3a0eae0784e3091d138915c8
Reviewed-on: http://gerrit.rockbox.org/566
Reviewed-by: Michael Sevakis <jethead71@rockbox.org>
Tested: Michael Sevakis <jethead71@rockbox.org>

1 files changed, 313 insertions, 138 deletions

diff --git a/firmware/common/unicode.c b/firmware/common/unicode.c
index 3ff1814c4b..954ad47e1d 100644
--- a/firmware/common/unicode.c
+++ b/firmware/common/unicode.c
@@ -28,161 +28,227 @@
 
 #include <stdio.h>
 #include "config.h"
+#include "system.h"
+#include "thread.h"
 #include "file.h"
 #include "debug.h"
 #include "rbunicode.h"
 #include "rbpaths.h"
+#include "pathfuncs.h"
+#include "core_alloc.h"
 
 #ifndef O_BINARY
 #define O_BINARY 0
 #endif
+#ifndef O_NOISODECODE
+#define O_NOISODECODE 0
+#endif
 
-static int default_codepage = 0;
-static int loaded_cp_table = 0;
-
-#ifdef HAVE_LCD_BITMAP
+#define getle16(p) (p[0] | (p[1] >> 8))
+#define getbe16(p) ((p[1] << 8) | p[0])
 
-#define MAX_CP_TABLE_SIZE  32768
-#define NUM_TABLES             5
+#if !defined (__PCTOOL__) && (CONFIG_PLATFORM & PLATFORM_NATIVE)
+/* Because file scanning uses the default CP table when matching entries,
+   on-demand loading is not feasible; we also must use the filesystem lock */
+#include "file_internal.h"
+#else /* APPLICATION */
+#ifdef __PCTOOL__
+#define yield()
+#endif
+#define open_noiso_internal open
+#endif /* !APPLICATION */
+
+#if 0 /* not needed just now (will probably end up a spinlock) */
+#include "mutex.h"
+static struct mutex cp_mutex SHAREDBSS_ATTR;
+#define cp_lock_init()   mutex_init(&cp_mutex)
+#define cp_lock_enter()  mutex_lock(&cp_mutex)
+#define cp_lock_leave()  mutex_unlock(&cp_mutex)
+#else
+#define cp_lock_init()   do {} while (0)
+#define cp_lock_enter()  asm volatile ("")
+#define cp_lock_leave()  asm volatile ("")
+#endif
 
-static const char * const filename[NUM_TABLES] =
+enum cp_tid
 {
-    CODEPAGE_DIR"/iso.cp",
-    CODEPAGE_DIR"/932.cp",  /* SJIS    */
-    CODEPAGE_DIR"/936.cp",  /* GB2312  */
-    CODEPAGE_DIR"/949.cp",  /* KSX1001 */
-    CODEPAGE_DIR"/950.cp"   /* BIG5    */
+    CP_TID_NONE = -1,
+    CP_TID_ISO,
+    CP_TID_932,
+    CP_TID_936,
+    CP_TID_949,
+    CP_TID_950,
 };
 
-static const char cp_2_table[NUM_CODEPAGES] =
+struct cp_info
 {
-    0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 3, 4, 5, 0
+    int8_t      tid;
+    const char  *filename;
+    const char  *name;
 };
 
-static const char * const name_codepages[NUM_CODEPAGES+1] =
-{
-    "ISO-8859-1",
-    "ISO-8859-7",
-    "ISO-8859-8",
-    "CP1251",
-    "ISO-8859-11",
-    "CP1256",
-    "ISO-8859-9",
-    "ISO-8859-2",
-    "CP1250",
-    "CP1252",
-    "SJIS",
-    "GB-2312",
-    "KSX-1001",
-    "BIG5",
-    "UTF-8",
-    "unknown"
-};
+#ifdef HAVE_LCD_BITMAP
 
-#if defined(APPLICATION) && defined(__linux__)
-static const char * const name_codepages_linux[NUM_CODEPAGES+1] =
-{
-    /* "ISO-8859-1" */ "iso8859-1",
-    /* "ISO-8859-7" */ "iso8859-7",
-    /* "ISO-8859-8" */ "iso8859-8",
-    /* "CP1251"     */ "cp1251",
-    /* "ISO-8859-11"*/ "iso8859-11",
-    /* "CP1256"     */ "cp1256",
-    /* "ISO-8859-9" */ "iso8859-9",
-    /* "ISO-8859-2" */ "iso8859-2",
-    /* "CP1250"     */ "cp1250",
-    /* "CP1252"     */ "iso8859-15", /* closest, linux doesnt have a codepage named cp1252 */
-    /* "SJIS"       */ "cp932",
-    /* "GB-2312"    */ "cp936",
-    /* "KSX-1001"   */ "cp949",
-    /* "BIG5"       */ "cp950",
-    /* "UTF-8"      */ "utf8",
-    /* "unknown"    */ "cp437"
-};
+#define MAX_CP_TABLE_SIZE  32768
 
-const char *get_current_codepage_name_linux(void)
+#define CPF_ISO "iso.cp"
+#define CPF_932 "932.cp"  /* SJIS    */
+#define CPF_936 "936.cp"  /* GB2312  */
+#define CPF_949 "949.cp"  /* KSX1001 */
+#define CPF_950 "950.cp"  /* BIG5    */
+
+static const struct cp_info cp_info[NUM_CODEPAGES+1] =
 {
-    if (default_codepage < 0 || default_codepage >= NUM_CODEPAGES)
-        return name_codepages_linux[NUM_CODEPAGES];
-    return name_codepages_linux[default_codepage];
-}
-#endif
+    [0 ... NUM_CODEPAGES] = { CP_TID_NONE, NULL   , "unknown"     },
+    [ISO_8859_1]          = { CP_TID_NONE, NULL   , "ISO-8859-1"  },
+    [ISO_8859_7]          = { CP_TID_ISO , CPF_ISO, "ISO-8859-7"  },
+    [ISO_8859_8]          = { CP_TID_ISO , CPF_ISO, "ISO-8859-8"  },
+    [WIN_1251]            = { CP_TID_ISO , CPF_ISO, "CP1251"      },
+    [ISO_8859_11]         = { CP_TID_ISO , CPF_ISO, "ISO-8859-11" },
+    [WIN_1256]            = { CP_TID_ISO , CPF_ISO, "CP1256"      },
+    [ISO_8859_9]          = { CP_TID_ISO , CPF_ISO, "ISO-8859-9"  },
+    [ISO_8859_2]          = { CP_TID_ISO , CPF_ISO, "ISO-8859-2"  },
+    [WIN_1250]            = { CP_TID_ISO , CPF_ISO, "CP1250"      },
+    [WIN_1252]            = { CP_TID_ISO , CPF_ISO, "CP1252"      },
+    [SJIS]                = { CP_TID_932 , CPF_932, "SJIS"        },
+    [GB_2312]             = { CP_TID_936 , CPF_936, "GB-2312"     },
+    [KSX_1001]            = { CP_TID_949 , CPF_949, "KSX-1001"    },
+    [BIG_5]               = { CP_TID_950 , CPF_950, "BIG5"        },
+    [UTF_8]               = { CP_TID_NONE, NULL   , "UTF-8"       },
+};
 
 #else /* !HAVE_LCD_BITMAP, reduced support */
 
 #define MAX_CP_TABLE_SIZE  768
-#define NUM_TABLES           1
 
-static const char * const filename[NUM_TABLES] = {
-    CODEPAGE_DIR"/isomini.cp"
-};
+#define CPF_ISOMINI "isomini.cp"
 
-static const char cp_2_table[NUM_CODEPAGES] =
+static const struct cp_info cp_info[NUM_CODEPAGES+1] =
 {
-    0, 1, 1, 1, 1, 1, 1, 0
+    [0 ... NUM_CODEPAGES] = { CP_TID_NONE, NULL       , "unknown"    },
+    [ISO_8859_1]          = { CP_TID_NONE, NULL       , "ISO-8859-1" },
+    [ISO_8859_7]          = { CP_TID_ISO , CPF_ISOMINI, "ISO-8859-7" },
+    [WIN_1251]            = { CP_TID_ISO , CPF_ISOMINI, "CP1251"     },
+    [ISO_8859_9]          = { CP_TID_ISO , CPF_ISOMINI, "ISO-8859-9" },
+    [ISO_8859_2]          = { CP_TID_ISO , CPF_ISOMINI, "ISO-8859-2" },
+    [WIN_1250]            = { CP_TID_ISO , CPF_ISOMINI, "CP1250"     },
+    [WIN_1252]            = { CP_TID_ISO , CPF_ISOMINI, "CP1252"     },
+    [UTF_8]               = { CP_TID_ISO , NULL       , "UTF-8"      },
 };
 
-static const char * const name_codepages[NUM_CODEPAGES+1] =
+#endif /* HAVE_LCD_BITMAP */
+
+static int default_cp = INIT_CODEPAGE;
+static int default_cp_tid = CP_TID_NONE;
+static int default_cp_handle = 0;
+static int volatile default_cp_table_ref = 0;
+
+static int loaded_cp_tid = CP_TID_NONE;
+static int volatile cp_table_ref = 0;
+#define CP_LOADING BIT_N(sizeof(int)*8-1) /* guard against multi loaders */
+
+/* non-default codepage table buffer (cannot be bufalloced! playback itself
+   may be making the load request) */
+static unsigned short codepage_table[MAX_CP_TABLE_SIZE+1];
+
+#if defined(APPLICATION) && defined(__linux__)
+static const char * const name_codepages_linux[NUM_CODEPAGES+1] =
 {
-    "ISO-8859-1",
-    "ISO-8859-7",
-    "CP1251",
-    "ISO-8859-9",
-    "ISO-8859-2",
-    "CP1250",
-    "CP1252",
-    "UTF-8",
-    "unknown"
+    [0 ... NUM_CODEPAGES] = "unknown",
+    [ISO_8859_1]          = "iso8859-1",
+    [ISO_8859_7]          = "iso8859-7",
+    [ISO_8859_8]          = "iso8859-8",
+    [WIN_1251]            = "cp1251",
+    [ISO_8859_11]         = "iso8859-11",
+    [WIN_1256]            = "cp1256",
+    [ISO_8859_9]          = "iso8859-9",
+    [ISO_8859_2]          = "iso8859-2",
+    [WIN_1250]            = "cp1250",
+    /* iso8859-15 is closest, linux doesnt have a codepage named cp1252 */
+    [WIN_1252]            = "iso8859-15",
+    [SJIS]                = "cp932",
+    [GB_2312]             = "cp936",
+    [KSX_1001]            = "cp949",
+    [BIG_5]               = "cp950",
+    [UTF_8]               = "utf8",
 };
 
-#endif
-
-static unsigned short codepage_table[MAX_CP_TABLE_SIZE];
+const char *get_current_codepage_name_linux(void)
+{
+    int cp = default_cp;
+    if (cp < 0 || cp>= NUM_CODEPAGES)
+        cp = NUM_CODEPAGES;
+    return name_codepages_linux[cp];
+}
+#endif /* defined(APPLICATION) && defined(__linux__) */
 
 static const unsigned char utf8comp[6] =
 {
     0x00, 0xC0, 0xE0, 0xF0, 0xF8, 0xFC
 };
 
-/* Load codepage file into memory */
-static int load_cp_table(int cp)
+static inline void cptable_tohw16(uint16_t *buf, unsigned int count)
 {
-    int i = 0;
-    int table = cp_2_table[cp];
-    int file, tablesize;
-    unsigned char tmp[2];
+#ifdef ROCKBOX_BIG_ENDIAN
+    for (unsigned int i = 0; i < count; i++)
+        buf[i] = letoh16(buf[i]);
+#endif
+    (void)buf; (void)count;
+}
 
-    if (table == 0 || table == loaded_cp_table)
-        return 1;
+static int move_callback(int handle, void *current, void *new)
+{
+    /* we don't keep a pointer but we have to stop it if this applies to a
+       buffer not yet swapped-in since it will likely be in use in an I/O
+       call */
+    return (handle != default_cp_handle || default_cp_table_ref != 0) ?
+                BUFLIB_CB_CANNOT_MOVE : BUFLIB_CB_OK;
+    (void)current; (void)new;
+}
 
-    file = open(filename[table-1], O_RDONLY|O_BINARY);
+static int alloc_and_load_cp_table(int cp, void *buf)
+{
+    static struct buflib_callbacks ops =
+        { .move_callback = move_callback };
 
-    if (file < 0) {
-        DEBUGF("Can't open codepage file: %s.cp\n", filename[table-1]);
+    /* alloc and read only if there is an associated file */
+    const char *filename = cp_info[cp].filename;
+    if (!filename)
         return 0;
+
+    char path[MAX_PATH];
+    if (path_append(path, CODEPAGE_DIR, filename, sizeof (path))
+        >= sizeof (path)) {
+        return -1;
     }
 
-    tablesize = filesize(file) / 2;
+    /* must be opened without a chance of reentering from FS code */
+    int fd = open_noiso_internal(path, O_RDONLY);
+    if (fd < 0)
+        return -1;
 
-    if (tablesize > MAX_CP_TABLE_SIZE) {
-        DEBUGF("Invalid codepage file: %s.cp\n", filename[table-1]);
-        close(file);
-        return 0;
-    }
+    off_t size = filesize(fd);
 
-    while (i < tablesize) {
-        if (!read(file, tmp, 2)) {
-            DEBUGF("Can't read from codepage file: %s.cp\n", 
-                    filename[table-1]);
-            loaded_cp_table = 0;
-            return 0;
+    if (size > 0 && size <= MAX_CP_TABLE_SIZE*2 &&
+        !(size % (off_t)sizeof (uint16_t))) {
+
+        /* if the buffer is provided, use that but don't alloc */
+        int handle = buf ? 0 : core_alloc_ex(filename, size, &ops);
+        if (handle > 0)
+            buf = core_get_data(handle);
+
+        if (buf && read(fd, buf, size) == size) {
+            close(fd);
+            cptable_tohw16(buf, size / sizeof (uint16_t));
+            return handle;
         }
-        codepage_table[i++] = (tmp[1] << 8) | tmp[0];
+
+        if (handle > 0)
+            core_free(handle);
     }
 
-    loaded_cp_table = table;
-    close(file);
-    return 1;
+    close(fd);
+    return -1;
 }
 
 /* Encode a UCS value as UTF-8 and return a pointer after this UTF-8 char. */
@@ -205,47 +271,96 @@ unsigned char* utf8encode(unsigned long ucs, unsigned char *utf8)
 unsigned char* iso_decode(const unsigned char *iso, unsigned char *utf8,
                           int cp, int count)
 {
-    unsigned short ucs, tmp;
+    uint16_t *table = NULL;
+
+    cp_lock_enter();
+
+    if (cp < 0 || cp >= NUM_CODEPAGES)
+        cp = default_cp;
 
-    if (cp == -1) /* use default codepage */
-        cp = default_codepage;
+    int tid = cp_info[cp].tid;
 
-    if (!load_cp_table(cp)) cp = 0;
+    while (1) {
+        if (tid == default_cp_tid) {
+            /* use default table */
+            if (default_cp_handle > 0) {
+                table = core_get_data(default_cp_handle);
+                default_cp_table_ref++;
+            }
+
+            break;
+        }
+
+        bool load = false;
+
+        if (tid == loaded_cp_tid) {
+            /* use loaded table */
+            if (!(cp_table_ref & CP_LOADING)) {
+                if (tid != CP_TID_NONE) {
+                    table = codepage_table;
+                    cp_table_ref++;
+                }
+
+                break;
+            }
+        } else if (cp_table_ref == 0) {
+            load = true;
+            cp_table_ref |= CP_LOADING;
+        }
+
+        /* alloc and load must be done outside the lock */
+        cp_lock_leave();
+
+        if (!load) {
+            yield();
+        } else if (alloc_and_load_cp_table(cp, codepage_table) < 0) {
+            cp = INIT_CODEPAGE; /* table may be clobbered now */
+            tid = cp_info[cp].tid;
+        }
+
+        cp_lock_enter();
+
+        if (load) {
+            loaded_cp_tid = tid;
+            cp_table_ref &= ~CP_LOADING;
+        }
+    }
+
+    cp_lock_leave();
 
     while (count--) {
+        unsigned short ucs, tmp;
+
         if (*iso < 128 || cp == UTF_8) /* Already UTF-8 */
             *utf8++ = *iso++;
 
         else {
-
-            /* cp tells us which codepage to convert from */
-            switch (cp) {
-                case ISO_8859_7:  /* Greek */
-                case WIN_1252:    /* Western European */
-                case WIN_1251:    /* Cyrillic */
-                case ISO_8859_9:  /* Turkish */
-                case ISO_8859_2:  /* Latin Extended */
-                case WIN_1250:    /* Central European */
-#ifdef HAVE_LCD_BITMAP
-                case ISO_8859_8:  /* Hebrew */
-                case ISO_8859_11: /* Thai */
-                case WIN_1256:    /* Arabic */
-#endif
+            /* tid tells us which table to use and how */
+            switch (tid) {
+                case CP_TID_ISO: /* Greek */
+                                 /* Hebrew */
+                                 /* Cyrillic */
+                                 /* Thai */
+                                 /* Arabic */
+                                 /* Turkish */
+                                 /* Latin Extended */
+                                 /* Central European */
+                                 /* Western European */
                     tmp = ((cp-1)*128) + (*iso++ - 128);
-                    ucs = codepage_table[tmp];
+                    ucs = table[tmp];
                     break;
 
 #ifdef HAVE_LCD_BITMAP
-                case SJIS: /* Japanese */
+                case CP_TID_932: /* Japanese */
                     if (*iso > 0xA0 && *iso < 0xE0) {
                         tmp = *iso++ | (0xA100 - 0x8000);
-                        ucs = codepage_table[tmp];
+                        ucs = table[tmp];
                         break;
                     }
 
-                case GB_2312:  /* Simplified Chinese */
-                case KSX_1001: /* Korean */
-                case BIG_5:    /* Traditional Chinese */
+                case CP_TID_936: /* Simplified Chinese */
+                case CP_TID_949: /* Korean */
+                case CP_TID_950: /* Traditional Chinese */
                     if (count < 1 || !iso[1]) {
                         ucs = *iso++;
                         break;
@@ -256,7 +371,7 @@ unsigned char* iso_decode(const unsigned char *iso, unsigned char *utf8,
                     tmp = *iso++ << 8;
                     tmp |= *iso++;
                     tmp -= 0x8000;
-                    ucs = codepage_table[tmp];
+                    ucs = table[tmp];
                     count--;
                     break;
 #endif /* HAVE_LCD_BITMAP */
@@ -271,6 +386,17 @@ unsigned char* iso_decode(const unsigned char *iso, unsigned char *utf8,
             utf8 = utf8encode(ucs, utf8);
         }
     }
+
+    if (table) {
+        cp_lock_enter();
+        if (table == codepage_table) {
+            cp_table_ref--;
+        } else {
+            default_cp_table_ref--;
+        }
+        cp_lock_leave();
+    }
+
     return utf8;
 }
 
@@ -288,7 +414,7 @@ unsigned char* utf16LEdecode(const unsigned char *utf16, unsigned char *utf8,
             utf16 += 4;
             count -= 2;
         } else {
-            ucs = (utf16[0] | (utf16[1] << 8));
+            ucs = getle16(utf16);
             utf16 += 2;
             count -= 1;
         }
@@ -310,7 +436,7 @@ unsigned char* utf16BEdecode(const unsigned char *utf16, unsigned char *utf8,
             utf16 += 4;
             count -= 2;
         } else {
-            ucs = (utf16[0] << 8) | utf16[1];
+            ucs = getbe16(utf16);
             utf16 += 2;
             count -= 1;
         }
@@ -400,8 +526,50 @@ const unsigned char* utf8decode(const unsigned char *utf8, unsigned short *ucs)
 
 void set_codepage(int cp)
 {
-    default_codepage = cp;
-    return;
+    if (cp < 0 || cp >= NUM_CODEPAGES)
+        cp = NUM_CODEPAGES;
+
+    /* load first then swap if load is successful, else just leave it; if
+       handle is 0 then we just free the current one; this won't happen often
+       thus we don't worry about reusing it and consequently avoid possible
+       clobbering of the existing one */
+
+    int handle = -1;
+    int tid = cp_info[cp].tid;
+
+    while (1) {
+        cp_lock_enter();
+
+        if (default_cp_tid == tid)
+            break;
+
+        if (handle >= 0 && default_cp_table_ref == 0) {
+            int hold = default_cp_handle;
+            default_cp_handle = handle;
+            handle = hold;
+            default_cp_tid = tid;
+            break;
+        }
+
+        /* alloc and load must be done outside the lock */
+        cp_lock_leave();
+
+        if (handle < 0 && (handle = alloc_and_load_cp_table(cp, NULL)) < 0)
+            return; /* OOM; change nothing */
+
+        yield();
+    }
+
+    default_cp = cp;
+    cp_lock_leave();
+
+    if (handle > 0)
+        core_free(handle);
+}
+
+int get_codepage(void)
+{
+    return default_cp;
 }
 
 /* seek to a given char in a utf8 string and
@@ -418,9 +586,16 @@ int utf8seek(const unsigned char* utf8, int offset)
     return pos;
 }
 
-const char* get_codepage_name(int cp)
+const char * get_codepage_name(int cp)
 {
-    if (cp < 0 || cp>= NUM_CODEPAGES)
-        return name_codepages[NUM_CODEPAGES];
-    return name_codepages[cp];
+    if (cp < 0 || cp >= NUM_CODEPAGES)
+        cp = NUM_CODEPAGES;
+    return cp_info[cp].name;
 }
+
+#if 0 /* not needed just now */
+void unicode_init(void)
+{
+    cp_lock_init();
+}
+#endif