add DISA/DIFF writing

this has only been tested with DIFF, specifically title database type files, but there's no reason it shouldn't work on all DISA/DIFF files

arm9/source/game/disadiff.c

@@ -1,6 +1,6 @@
 #include "disadiff.h"
 #include "image.h"
-#include "vff.h"
+#include "sha.h"
 
 #define GET_DPFS_BIT(b, lvl) (((((u32*) (void*) lvl)[b >> 5]) >> (31 - (b % 32))) & 1)
 
@@ -9,7 +9,7 @@ static FIL ddfile;
 static FIL* ddfp = NULL;
 
 inline static u32 DisaDiffSize(const TCHAR* path) {
-    return path ? fvx_qsize(path) : GetMountSize();
+    return ddfp ? fvx_size(ddfp) : (path ? fvx_qsize(path) : GetMountSize());
 }
 
 inline static FRESULT DisaDiffOpen(const TCHAR* path) {
@@ -17,7 +17,7 @@ inline static FRESULT DisaDiffOpen(const TCHAR* path) {
     
     ddfp = NULL;
     if (path) {
-        res = fvx_open(&ddfile, path, FA_READ | FA_OPEN_EXISTING);
+        res = fvx_open(&ddfile, path, FA_READ | FA_WRITE | FA_OPEN_EXISTING);
         if (res == FR_OK) ddfp = &ddfile;
     } else if (!GetMountState()) res = FR_DENIED;
     
@@ -36,6 +36,18 @@ inline static FRESULT DisaDiffRead(void* buf, UINT btr, UINT ofs) {
     } else return (ReadImageBytes(buf, (u64) ofs, (u64) btr) == 0) ? FR_OK : FR_DENIED;
 }
 
+inline static FRESULT DisaDiffWrite(const void* buf, UINT btw, UINT ofs) {
+    if (ddfp) {
+        FRESULT res;
+        UINT bw;
+        if ((fvx_tell(ddfp) != ofs) &&
+            (fvx_lseek(ddfp, ofs) != FR_OK)) return FR_DENIED;
+        res = fvx_write(ddfp, buf, btw, &bw);
+        if ((res == FR_OK) && (bw != btw)) res = FR_DENIED;
+        return res;
+    } else return (WriteImageBytes(buf, (u64) ofs, (u64) btw) == 0) ? FR_OK : FR_DENIED;
+}
+
 inline static FRESULT DisaDiffClose() {
     if (ddfp) {
         ddfp = NULL;
@@ -48,21 +60,32 @@ inline static FRESULT DisaDiffQRead(const TCHAR* path, void* buf, UINT ofs, UINT
     else return (ReadImageBytes(buf, (u64) ofs, (u64) btr) == 0) ? FR_OK : FR_DENIED;
 }
 
+inline static FRESULT DisaDiffQWrite(const TCHAR* path, const void* buf, UINT ofs, UINT btw) {
+    if (path) return fvx_qwrite(path, buf, ofs, btw, NULL);
+    else return (WriteImageBytes(buf, (u64) ofs, (u64) btw) == 0) ? FR_OK : FR_DENIED;
+}
 
-u32 GetDisaDiffReaderInfo(const char* path, DisaDiffReaderInfo* info, bool partitionB) {
+void SetDisaDiffFile(FIL* fp) {
+    ddfp = fp;
+}
+
+u32 GetDisaDiffRWInfo(const char* path, DisaDiffRWInfo* info, bool partitionB) {
     const u8 disa_magic[] = { DISA_MAGIC };
     const u8 diff_magic[] = { DIFF_MAGIC };
     const u8 ivfc_magic[] = { IVFC_MAGIC };
     const u8 dpfs_magic[] = { DPFS_MAGIC };
     const u8 difi_magic[] = { DIFI_MAGIC };
     
+    bool already_open = ddfp != NULL;
+    
     // reset reader info
-    memset(info, 0x00, sizeof(DisaDiffReaderInfo));
+    memset(info, 0x00, sizeof(DisaDiffRWInfo));
     
     // get file size, header at header offset
     u32 file_size = DisaDiffSize(path);
     u8 header[0x100];
-    if (DisaDiffQRead(path, header, 0x100, 0x100) != FR_OK) return 1;
+    if ((already_open ? DisaDiffRead(header, 0x100, 0x100) : DisaDiffQRead(path, header, 0x100, 0x100)) != FR_OK)
+        return 1;
     
     // DISA/DIFF header: find partition offset & size and DIFI descriptor
     u32 offset_partition = 0;
@@ -81,29 +104,36 @@ u32 GetDisaDiffReaderInfo(const char* path, DisaDiffReaderInfo* info, bool parti
             size_partition = (u32) disa->size_partitionB;
             offset_difi += (u32) disa->offset_descB;
         }
+        info->offset_partition_hash = 0x16C;
     } else if (memcmp(header, diff_magic, 8) == 0) { // DIFF file
-        if (partitionB) return 1;
+        if (partitionB)
+            return 1;
         DiffHeader* diff = (DiffHeader*) (void*) header;
         offset_partition = (u32) diff->offset_partition;
         size_partition = (u32) diff->size_partition;
         offset_difi = (diff->active_table) ? diff->offset_table1 : diff->offset_table0;
+        info->offset_partition_hash = 0x134;
+    } else {
+        return 1;
     }
     
     // check the output so far
-    if (!offset_difi || (offset_difi + sizeof(DifiStruct) > file_size) ||
+    if (!offset_difi || (offset_difi + sizeof(DifiStruct) > file_size) || (offset_partition + size_partition > file_size))
-        (offset_partition + size_partition > file_size))
         return 1;
         
+    info->offset_difi = offset_difi;
     // read DIFI struct from filr
-    DifiStruct difis;
+    const DifiStruct difis;
-    if (DisaDiffQRead(path, &difis, offset_difi, sizeof(DifiStruct)) != FR_OK) return 1;
+    if ((already_open ? DisaDiffRead((DifiStruct*) &difis, sizeof(DifiStruct), offset_difi) : DisaDiffQRead(path, (DifiStruct*) &difis, offset_difi, sizeof(DifiStruct))) != FR_OK)
+        return 1;
+    
     if ((memcmp(difis.difi.magic, difi_magic, 8) != 0) ||
         (memcmp(difis.ivfc.magic, ivfc_magic, 8) != 0) ||
         (memcmp(difis.dpfs.magic, dpfs_magic, 8) != 0))
         return 1;
     
     // check & get data from DIFI header
-    DifiHeader* difi = &(difis.difi);
+    const DifiHeader* difi = &(difis.difi);
     if ((difi->offset_ivfc != sizeof(DifiHeader)) ||
         (difi->size_ivfc != sizeof(IvfcDescriptor)) ||
         (difi->offset_dpfs != difi->offset_ivfc + difi->size_ivfc) ||
@@ -115,9 +145,11 @@ u32 GetDisaDiffReaderInfo(const char* path, DisaDiffReaderInfo* info, bool parti
     info->dpfs_lvl1_selector = difi->dpfs_lvl1_selector;
     info->ivfc_use_extlvl4 = difi->ivfc_use_extlvl4;
     info->offset_ivfc_lvl4 = (u32) (offset_partition + difi->ivfc_offset_extlvl4);
+    info->offset_master_hash = (u32) difi->offset_hash;
+    info->size_master_hash = (u32) difi->size_hash;
     
     // check & get data from DPFS descriptor
-    DpfsDescriptor* dpfs = &(difis.dpfs);
+    const DpfsDescriptor* dpfs = &(difis.dpfs);
     if ((dpfs->offset_lvl1 + dpfs->size_lvl1 > dpfs->offset_lvl2) ||
         (dpfs->offset_lvl2 + dpfs->size_lvl2 > dpfs->offset_lvl3) ||
         (dpfs->offset_lvl3 + dpfs->size_lvl3 > size_partition) ||
@@ -135,32 +167,46 @@ u32 GetDisaDiffReaderInfo(const char* path, DisaDiffReaderInfo* info, bool parti
     info->log_dpfs_lvl3 = (u32) dpfs->log_lvl3;
         
     // check & get data from IVFC descriptor
-    IvfcDescriptor* ivfc = &(difis.ivfc);
+    const IvfcDescriptor* ivfc = &(difis.ivfc);
     if ((ivfc->size_hash != difi->size_hash) ||
         (ivfc->size_ivfc != sizeof(IvfcDescriptor)) ||
         (ivfc->offset_lvl1 + ivfc->size_lvl1 > ivfc->offset_lvl2) ||
         (ivfc->offset_lvl2 + ivfc->size_lvl2 > ivfc->offset_lvl3) ||
         (ivfc->offset_lvl3 + ivfc->size_lvl3 > dpfs->size_lvl3))
         return 1;
+        
     if (!info->ivfc_use_extlvl4) {
         if ((ivfc->offset_lvl3 + ivfc->size_lvl3 > ivfc->offset_lvl4) ||
             (ivfc->offset_lvl4 + ivfc->size_lvl4 > dpfs->size_lvl3))
             return 1;
+        
         info->offset_ivfc_lvl4 = (u32) ivfc->offset_lvl4;
-    } else if (info->offset_ivfc_lvl4 + ivfc->size_lvl4 > offset_partition + size_partition) {
+    } else if (info->offset_ivfc_lvl4 + ivfc->size_lvl4 > offset_partition + size_partition)
         return 1;
-    }
+    
+    info->log_ivfc_lvl1 = (u32) ivfc->log_lvl1;
+    info->log_ivfc_lvl2 = (u32) ivfc->log_lvl2;
+    info->log_ivfc_lvl3 = (u32) ivfc->log_lvl3;
+    info->log_ivfc_lvl4 = (u32) ivfc->log_lvl4;
+    info->offset_ivfc_lvl1 = (u32) ivfc->offset_lvl1;
+    info->offset_ivfc_lvl2 = (u32) ivfc->offset_lvl2;
+    info->offset_ivfc_lvl3 = (u32) ivfc->offset_lvl3;
+    info->size_ivfc_lvl1 = (u32) ivfc->size_lvl1;
+    info->size_ivfc_lvl2 = (u32) ivfc->size_lvl2;
+    info->size_ivfc_lvl3 = (u32) ivfc->size_lvl3;
     info->size_ivfc_lvl4 = (u32) ivfc->size_lvl4;
     
     return 0;
 }
 
-u32 BuildDisaDiffDpfsLvl2Cache(const char* path, DisaDiffReaderInfo* info, u8* cache, u32 cache_size) {
+u32 BuildDisaDiffDpfsLvl2Cache(const char* path, const DisaDiffRWInfo* info, u8* cache, u32 cache_size) {
     const u32 min_cache_bits = (info->size_dpfs_lvl3 + (1 << info->log_dpfs_lvl3) - 1) >> info->log_dpfs_lvl3;
     const u32 min_cache_size = ((min_cache_bits + 31) >> (3 + 2)) << 2;
     const u32 offset_lvl1 = info->offset_dpfs_lvl1 + ((info->dpfs_lvl1_selector) ? info->size_dpfs_lvl1 : 0);
     
-    // safety (this still assumes all the checks from GetDisaDiffReaderInfo())
+    bool already_open = ddfp != NULL;
+    
+    // safety (this still assumes all the checks from GetDisaDiffRWInfo())
     if (info->ivfc_use_extlvl4 ||
         (cache_size < min_cache_size) ||
         (min_cache_size > info->size_dpfs_lvl2) ||
@@ -172,7 +218,7 @@ u32 BuildDisaDiffDpfsLvl2Cache(const char* path, DisaDiffReaderInfo* info, u8* c
     if (!lvl1) return 1; // this is never more than 8 byte in reality -___-
     
     // open file pointer
-    if (DisaDiffOpen(path) != FR_OK) {
+    if (!already_open && (DisaDiffOpen(path) != FR_OK)) {
         free(lvl1);
         return 1;
     }
@@ -197,40 +243,15 @@ u32 BuildDisaDiffDpfsLvl2Cache(const char* path, DisaDiffReaderInfo* info, u8* c
         }
     }
     
-    info->dpfs_lvl2_cache = cache;
+    ((DisaDiffRWInfo*) info)->dpfs_lvl2_cache = cache;
     free(lvl1);
+    if (!already_open)
         DisaDiffClose();
     return ret;
 }
 
-u32 ReadDisaDiffIvfcLvl4(const char* path, DisaDiffReaderInfo* info, u32 offset, u32 size, void* buffer) {
+static u32 ReadDisaDiffDpfsLvl3(const DisaDiffRWInfo* info, u32 offset, u32 size, void* buffer) { // assumes file is already open
-    // data: full DISA/DIFF file in memory
+    const u32 offset_start = offset;
-    // offset: offset inside IVFC lvl4
-    
-    // DisaDiffReaderInfo not provided?
-    DisaDiffReaderInfo info_l;
-    u8* cache = NULL;
-    if (!info) {
-        info = &info_l;
-        if (GetDisaDiffReaderInfo(path, info, false) != 0) return 0;
-        cache = malloc(info->size_dpfs_lvl2);
-        if (!cache) return 0;
-        if (BuildDisaDiffDpfsLvl2Cache(path, info, cache, info->size_dpfs_lvl2) != 0) {
-            free(cache);
-            return 0;
-        }
-    }
-   
-    // sanity checks - offset & size
-    if (offset > info->size_ivfc_lvl4) return 0;
-    else if (offset + size > info->size_ivfc_lvl4) size = info->size_ivfc_lvl4 - offset;
-    
-    if (info->ivfc_use_extlvl4) {
-        // quick reading in case of external IVFC lvl4
-        if (DisaDiffQRead(path, buffer, info->offset_ivfc_lvl4 + offset, size) != FR_OK) size = 0;
-    } else {
-        // full reading in standard case
-        const u32 offset_start = info->offset_ivfc_lvl4 + offset;
     const u32 offset_end = offset_start + size;
     const u8* lvl2 = info->dpfs_lvl2_cache;
     const u32 offset_lvl3_0 = info->offset_dpfs_lvl3;
@@ -241,9 +262,6 @@ u32 ReadDisaDiffIvfcLvl4(const char* path, DisaDiffReaderInfo* info, u32 offset,
     u32 read_end = read_start;
     u32 bit_state = 0;
     
-        // open file pointer
-        if (DisaDiffOpen(path) != FR_OK) size = 0;
-
     // full reading below
     while (size && (read_start < offset_end)) {
         // read bits until bit_state does not match
@@ -259,16 +277,297 @@ u32 ReadDisaDiffIvfcLvl4(const char* path, DisaDiffReaderInfo* info, u32 offset,
             const u32 pos_f = (bit_state ? offset_lvl3_1 : offset_lvl3_0) + read_start;
             const u32 pos_b = read_start - offset_start;
             const u32 btr = read_end - read_start;
-                if (DisaDiffRead((u8*) buffer + pos_b, btr, pos_f) != FR_OK) size = 0;
+            if (DisaDiffRead(((u8*) buffer) + pos_b, btr, pos_f) != FR_OK) size = 0;
             read_start = read_end;
         }
         // flip the bit_state
         bit_state = ~bit_state & 0x1;
     }
     
-        DisaDiffClose();
+    return size;
 }
 
+static u32 WriteDisaDiffDpfsLvl3(const DisaDiffRWInfo* info, u32 offset, u32 size, const void* buffer) { // assumes file is already open, does not fix hashes
+    const u32 offset_start = offset;
+    const u32 offset_end = offset_start + size;
+    const u8* lvl2 = info->dpfs_lvl2_cache;
+    const u32 offset_lvl3_0 = info->offset_dpfs_lvl3;
+    const u32 offset_lvl3_1 = offset_lvl3_0 + info->size_dpfs_lvl3;
+    const u32 log_lvl3 = info->log_dpfs_lvl3;
+    
+    u32 write_start = offset_start;
+    u32 write_end = write_start;
+    u32 bit_state = 0;
+    
+    // full reading below
+    while (size && (write_start < offset_end)) {
+        // write bits until bit_state does not match
+        // idx_lvl2 is a bit offset
+        u32 idx_lvl2 = write_end >> log_lvl3;
+        if (GET_DPFS_BIT(idx_lvl2, lvl2) == bit_state) {
+            write_end = (idx_lvl2+1) << log_lvl3;
+            if (write_end >= offset_end) write_end = offset_end;
+            else continue;
+        }
+        // write data if there is any
+        if (write_start < write_end) {
+            const u32 pos_f = (bit_state ? offset_lvl3_1 : offset_lvl3_0) + write_start;
+            const u32 pos_b = write_start - offset_start;
+            const u32 btw = write_end - write_start;
+            if (DisaDiffWrite(((u8*) buffer) + pos_b, btw, pos_f) != FR_OK) size = 0;
+            write_start = write_end;
+        }
+        // flip the bit_state
+        bit_state = ~bit_state & 0x1;
+    }
+    
+    return size;
+}
+
+u32 FixDisaDiffIvfcHashChain(const DisaDiffRWInfo* info, u32 offset, u32 size) { // offset relative to start of ivfc lvl4. assumes file is already open.
+    u32 lvl4_offset = (offset >> info->log_ivfc_lvl4) << info->log_ivfc_lvl4; // align starting offset
+    u32 lvl4_size = size + offset - lvl4_offset; // increase size by the amount starting offset decreased when aligned
+    const u32 lvl4_block_size = 1 << info->log_ivfc_lvl4;
+    u32 lvl4_read_size = lvl4_block_size;
+    u32 lvl3_offset = (((lvl4_offset >> info->log_ivfc_lvl4) * 0x20) >> info->log_ivfc_lvl3) << info->log_ivfc_lvl3;
+    u32 lvl3_size = ((lvl4_size >> info->log_ivfc_lvl4) + (((lvl4_size % lvl4_block_size) == 0) ? 0 : 1)) * 0x20;
+    const u32 lvl3_block_size = 1 << info->log_ivfc_lvl3;
+    u32 lvl3_read_size = lvl3_block_size;
+    u32 lvl2_offset = (((lvl3_offset >> info->log_ivfc_lvl3) * 0x20) >> info->log_ivfc_lvl2) << info->log_ivfc_lvl2;
+    u32 lvl2_size = ((lvl3_size >> info->log_ivfc_lvl3) + (((lvl3_size % lvl3_block_size) == 0) ? 0 : 1)) * 0x20;
+    const u32 lvl2_block_size = 1 << info->log_ivfc_lvl2;
+    u32 lvl2_read_size = lvl2_block_size;
+    u32 lvl1_offset = (((lvl2_offset >> info->log_ivfc_lvl2) * 0x20) >> info->log_ivfc_lvl1) << info->log_ivfc_lvl1;
+    u32 lvl1_size = ((lvl2_size >> info->log_ivfc_lvl2) + (((lvl2_size % lvl2_block_size) == 0) ? 0 : 1)) * 0x20;
+    const u32 lvl1_block_size = 1 << info->log_ivfc_lvl1;
+    u32 lvl1_read_size = lvl1_block_size;
+    
+    u8* buf;
+    u8 shabuf[0x20];
+    
+    if (!(buf = malloc(lvl4_block_size)))
+        return 1;
+    
+    
+    while (lvl4_size > 0)
+    {
+        if (lvl4_offset + lvl4_block_size > info->size_ivfc_lvl4)
+        {
+            memset(buf, 0, lvl4_block_size);
+            lvl4_read_size -= (lvl4_offset + lvl4_block_size - info->size_ivfc_lvl4);
+        }
+        
+        if (info->ivfc_use_extlvl4 ? (DisaDiffRead(buf, lvl4_read_size, lvl4_offset + info->offset_ivfc_lvl4) != FR_OK) :
+            (ReadDisaDiffDpfsLvl3(info, lvl4_offset + info->offset_ivfc_lvl4, lvl4_read_size, buf) != lvl4_read_size))
+        {
+            free(buf);            
+            return 1;
+        }
+        
+        sha_quick(shabuf, buf, lvl4_block_size, SHA256_MODE);
+        
+        if (WriteDisaDiffDpfsLvl3(info, info->offset_ivfc_lvl3 + ((lvl4_offset >> info->log_ivfc_lvl4) * 0x20), 0x20, shabuf) != 0x20)
+        {
+            free(buf);
+            return 1;
+        }
+        
+        lvl4_offset += lvl4_block_size;
+        lvl4_size = ((lvl4_size < lvl4_block_size) ? 0 : (lvl4_size - lvl4_block_size));
+    }
+    
+    free(buf);
+    
+    
+    if (!(buf = malloc(lvl3_block_size)))
+        return 1;
+    
+    while (lvl3_size > 0)
+    {
+        if (lvl3_offset + lvl3_block_size > info->size_ivfc_lvl3)
+        {
+            memset(buf, 0, lvl3_block_size);
+            lvl3_read_size -= (lvl3_offset + lvl3_block_size - info->size_ivfc_lvl3);
+        }
+        
+        if (ReadDisaDiffDpfsLvl3(info, lvl3_offset + info->offset_ivfc_lvl3, lvl3_read_size, buf) != lvl3_read_size)
+        {
+            free(buf);
+            return 1;
+        }
+        
+        sha_quick(shabuf, buf, lvl3_block_size, SHA256_MODE);
+        
+        if (WriteDisaDiffDpfsLvl3(info, info->offset_ivfc_lvl2 + ((lvl3_offset >> info->log_ivfc_lvl3) * 0x20), 0x20, shabuf) != 0x20)
+        {
+            free(buf);
+            return 1;
+        }
+        
+        lvl3_offset += lvl3_block_size;
+        lvl3_size = ((lvl3_size < lvl3_block_size) ? 0 : (lvl3_size - lvl3_block_size));
+    }
+    
+    free(buf);
+    
+    
+    if (!(buf = malloc(lvl2_block_size)))
+        return 1;
+    
+    while (lvl2_size > 0)
+    {
+        if (lvl2_offset + lvl2_block_size > info->size_ivfc_lvl2)
+        {
+            memset(buf, 0, lvl2_block_size);
+            lvl2_read_size -= (lvl2_offset + lvl2_block_size - info->size_ivfc_lvl2);
+        }
+        
+        if (ReadDisaDiffDpfsLvl3(info, lvl2_offset + info->offset_ivfc_lvl2, lvl2_read_size, buf) != lvl2_read_size)
+        {
+            free(buf);
+            return 1;
+        }
+        
+        sha_quick(shabuf, buf, lvl2_block_size, SHA256_MODE);
+        
+        if (WriteDisaDiffDpfsLvl3(info, info->offset_ivfc_lvl1 + ((lvl2_offset >> info->log_ivfc_lvl2) * 0x20), 0x20, shabuf) != 0x20)
+        {
+            free(buf);
+            return 1;
+        }
+        
+        lvl2_offset += lvl2_block_size;
+        lvl2_size = ((lvl2_size < lvl2_block_size) ? 0 : (lvl2_size - lvl2_block_size));
+    }
+    
+    free(buf);
+    
+    
+    if (!(buf = malloc(lvl1_block_size)))
+        return 1;
+    
+    while (lvl1_size > 0)
+    {
+        if (lvl1_offset + lvl1_block_size > info->size_ivfc_lvl1)
+        {
+            memset(buf, 0, lvl1_block_size);
+            lvl1_read_size -= (lvl1_offset + lvl1_block_size - info->size_ivfc_lvl1);
+        }
+        
+        if (ReadDisaDiffDpfsLvl3(info, lvl1_offset + info->offset_ivfc_lvl1, lvl1_read_size, buf) != lvl1_read_size)
+        {
+            free(buf);
+            return 1;
+        }
+        
+        sha_quick(shabuf, buf, lvl1_block_size, SHA256_MODE);
+        
+        if (DisaDiffWrite(shabuf, 0x20, info->offset_difi + info->offset_master_hash + ((lvl1_offset >> info->log_ivfc_lvl1) * 0x20)) != FR_OK)
+        {
+            free(buf);
+            return 1;
+        }
+        
+        lvl1_offset += lvl1_block_size;
+        lvl1_size = ((lvl1_size < lvl1_block_size) ? 0 : (lvl1_size - lvl1_block_size));
+    }
+    
+    free(buf);
+    
+    
+    if (!(buf = malloc(info->offset_master_hash + info->size_master_hash)))
+        return 1;
+    
+    if (DisaDiffRead(buf, info->offset_master_hash + info->size_master_hash, info->offset_difi) != FR_OK)
+    {
+        free(buf);
+        return 1;
+    }
+    
+    sha_quick(shabuf, buf, info->offset_master_hash + info->size_master_hash, SHA256_MODE);
+    
+    free(buf);
+    
+    if (DisaDiffWrite(shabuf, 0x20, info->offset_partition_hash) != FR_OK)
+        return 1;
+    
+    return 0;
+}
+    
+u32 ReadDisaDiffIvfcLvl4(const char* path, const DisaDiffRWInfo* info, u32 offset, u32 size, void* buffer) { // offset: offset inside IVFC lvl4
+    bool already_open = ddfp != NULL;
+    
+    // DisaDiffRWInfo not provided?
+    DisaDiffRWInfo info_l;
+    u8* cache = NULL;
+    if (!info) {
+        info = &info_l;
+        if (GetDisaDiffRWInfo(path, (DisaDiffRWInfo*) info, false) != 0) return 0;
+        cache = malloc(info->size_dpfs_lvl2);
+        if (!cache) return 0;
+        if (BuildDisaDiffDpfsLvl2Cache(path, info, cache, info->size_dpfs_lvl2) != 0) {
+            free(cache);
+            return 0;
+        }
+    }
+    
+    // open file pointer
+    if (!already_open && (DisaDiffOpen(path) != FR_OK))
+        size = 0;
+    
+    // sanity checks - offset & size
+    if (offset > info->size_ivfc_lvl4) return 0;
+    else if (offset + size > info->size_ivfc_lvl4) size = info->size_ivfc_lvl4 - offset;
+    
+    if (info->ivfc_use_extlvl4) {
+        if (DisaDiffRead(buffer, size, info->offset_ivfc_lvl4 + offset) != FR_OK)
+            size = 0;
+    } else {
+        size = ReadDisaDiffDpfsLvl3(info, info->offset_ivfc_lvl4 + offset, size, buffer);
+    }
+
+    if (!already_open) DisaDiffClose();
+    if (cache) free(cache);
+    return size;
+}
+
+u32 WriteDisaDiffIvfcLvl4(const char* path, const DisaDiffRWInfo* info, u32 offset, u32 size, const void* buffer) { // offset: offset inside IVFC lvl4. cmac still needs fixed after calling this.
+    bool already_open = ddfp != NULL;
+    
+    // DisaDiffRWInfo not provided?
+    DisaDiffRWInfo info_l;
+    u8* cache = NULL;
+    if (!info) {
+        info = &info_l;
+        if (GetDisaDiffRWInfo(path, (DisaDiffRWInfo*) info, false) != 0)
+            return 0;
+        cache = malloc(info->size_dpfs_lvl2);
+        if (!cache) return 0;
+        if (BuildDisaDiffDpfsLvl2Cache(path, info, cache, info->size_dpfs_lvl2) != 0) {
+            free(cache);
+            return 0;
+        }
+    }
+    
+    // sanity check - offset & size
+    if (offset + size > info->size_ivfc_lvl4)
+        return 0;
+    
+    // open file pointer
+    if (!already_open && (DisaDiffOpen(path) != FR_OK))
+        size = 0;
+    
+    if (info->ivfc_use_extlvl4) {
+        if (DisaDiffWrite(buffer, size, info->offset_ivfc_lvl4 + offset) != FR_OK)
+            size = 0;
+    } else {
+        size = WriteDisaDiffDpfsLvl3(info, info->offset_ivfc_lvl4 + offset, size, buffer);
+    }
+    
+    if ((size != 0) && (FixDisaDiffIvfcHashChain(info, offset, size) != 0))
+        size = 0;
+    
+    if (!already_open) DisaDiffClose();
     if (cache) free(cache);
     return size;
 }

arm9/source/game/disadiff.h

@@ -1,6 +1,7 @@
 #pragma once
 
 #include "common.h"
+#include "vff.h"
 
 
 // info taken from here:
@@ -107,8 +108,12 @@ typedef struct {
     u8 padding[4]; // all zeroes when encrypted
 } PACKED_STRUCT DifiStruct;
 
-// condensed info to enable reading IVFC lvl4
+// condensed info to enable reading/writing IVFC lvl4
 typedef struct {
+    u32 offset_partition_hash;
+    u32 offset_difi;
+    u32 offset_master_hash; // relative to start of difi
+    u32 size_master_hash;
     u32 offset_dpfs_lvl1; // relative to start of file
     u32 offset_dpfs_lvl2; // relative to start of file
     u32 offset_dpfs_lvl3; // relative to start of file
@@ -117,13 +122,25 @@ typedef struct {
     u32 size_dpfs_lvl3;
     u32 log_dpfs_lvl2;
     u32 log_dpfs_lvl3;
+    u32 log_ivfc_lvl1;
+    u32 log_ivfc_lvl2;
+    u32 log_ivfc_lvl3;
+    u32 log_ivfc_lvl4;
+    u32 offset_ivfc_lvl1; // relative to DPFS lvl3
+    u32 offset_ivfc_lvl2; // relative to DPFS lvl3
+    u32 offset_ivfc_lvl3; // relative to DPFS lvl3
     u32 offset_ivfc_lvl4; // relative to DPFS lvl3 if not external
+    u32 size_ivfc_lvl1;
+    u32 size_ivfc_lvl2;
+    u32 size_ivfc_lvl3;
     u32 size_ivfc_lvl4;
     u8  dpfs_lvl1_selector;
     u8  ivfc_use_extlvl4;
     u8* dpfs_lvl2_cache; // optional, NULL when unused
-} PACKED_STRUCT DisaDiffReaderInfo;
+} __attribute__((packed)) DisaDiffRWInfo;
 
-u32 GetDisaDiffReaderInfo(const char* path, DisaDiffReaderInfo* info, bool partitionB);
+void SetDisaDiffFile(FIL* fp); // Pass an already open file. Other calls will ignore path argument if a non-NULL was last passed to this function.
-u32 BuildDisaDiffDpfsLvl2Cache(const char* path, DisaDiffReaderInfo* info, u8* cache, u32 cache_size);
+u32 GetDisaDiffRWInfo(const char* path, DisaDiffRWInfo* info, bool partitionB);
-u32 ReadDisaDiffIvfcLvl4(const char* path, DisaDiffReaderInfo* info, u32 offset, u32 size, void* buffer);
+u32 BuildDisaDiffDpfsLvl2Cache(const char* path, const DisaDiffRWInfo* info, u8* cache, u32 cache_size);
+u32 ReadDisaDiffIvfcLvl4(const char* path, const DisaDiffRWInfo* info, u32 offset, u32 size, void* buffer);
+u32 WriteDisaDiffIvfcLvl4(const char* path, const DisaDiffRWInfo* info, u32 offset, u32 size, const void* buffer);

arm9/source/utils/gameutil.c

@@ -1843,9 +1843,9 @@ u32 ExtractDataFromDisaDiff(const char* path) {
     if (!CheckWritePermissions(dest)) return 1;
     
     // prepare DISA / DIFF read
-    DisaDiffReaderInfo info;
+    DisaDiffRWInfo info;
     u8* lvl2_cache = NULL;
-    if ((GetDisaDiffReaderInfo(path, &info, false) != 0) ||
+    if ((GetDisaDiffRWInfo(path, &info, false) != 0) ||
         !(lvl2_cache = (u8*) malloc(info.size_dpfs_lvl2)) ||
         (BuildDisaDiffDpfsLvl2Cache(path, &info, lvl2_cache, info.size_dpfs_lvl2) != 0)) {
         if (lvl2_cache) free(lvl2_cache);

arm9/source/virtual/vtickdb.c

@@ -43,7 +43,7 @@ static const VirtualFile vTickDbFileTemplates[] = {
 
 static TickDbInfo* tick_info = NULL;
 static u8* lvl2_cache = NULL;
-static DisaDiffReaderInfo diff_info;
+static DisaDiffRWInfo diff_info;
 static bool scanned_raw = false;
 
 
@@ -130,7 +130,7 @@ u64 InitVTickDbDrive(void) { // prerequisite: ticket.db mounted as image
     memset(tick_info, 0, 16);
     
     // setup DIFF reading
-    if ((GetDisaDiffReaderInfo(NULL, &diff_info, false) != 0) ||
+    if ((GetDisaDiffRWInfo(NULL, &diff_info, false) != 0) ||
         !(lvl2_cache = (u8*) malloc(diff_info.size_dpfs_lvl2)) ||
         (BuildDisaDiffDpfsLvl2Cache(NULL, &diff_info, lvl2_cache, diff_info.size_dpfs_lvl2) != 0)) {
         DeinitVTickDbDrive();