lxfs: read/write blocks and block chains

fs/lxfs/src/blockio.c

@@ -0,0 +1,75 @@
+/*
+ * luxOS - a unix-like operating system
+ * Omar Elghoul, 2024
+ * 
+ * lxfs: Driver for the lxfs file system
+ */
+
+#include <lxfs/lxfs.h>
+#include <unistd.h>
+
+/* lxfsReadBlock(): reads a block on a mounted lxfs partition
+ * params: mp - mountpoint
+ * params: block - block number
+ * params: buffer - buffer to read into
+ * returns: zero on success
+ */
+
+int lxfsReadBlock(Mountpoint *mp, uint64_t block, void *buffer) {
+    lseek(mp->fd, block * mp->blockSizeBytes, SEEK_SET);
+    return !(read(mp->fd, buffer, mp->blockSizeBytes) == mp->blockSizeBytes);
+}
+
+/* lxfsWriteBlock(): writes a block to a mounted lxfs partition
+ * params: mp - mountpoint
+ * params: block - block number
+ * params: buffer - buffer to write from
+ * returns: zero on success
+ */
+
+int lxfsWriteBlock(Mountpoint *mp, uint64_t block, const void *buffer) {
+    lseek(mp->fd, block * mp->blockSizeBytes, SEEK_SET);
+    return !(write(mp->fd, buffer, mp->blockSizeBytes) == mp->blockSizeBytes);
+}
+
+/* lxfsNextBlock(): returns the next block in a chain of blocks
+ * params: mp - mountpoint
+ * params: block - current block number
+ * returns: next block number, zero on fail
+ */
+
+uint64_t lxfsNextBlock(Mountpoint *mp, uint64_t block) {
+    // read the relevant part of the block table
+    uint64_t tableBlock = block / (mp->blockSizeBytes / 8);
+    tableBlock += 33;   // the first 33 blocks are reserved
+    uint64_t tableIndex = block % (mp->blockSizeBytes % 8);
+
+    if(lxfsReadBlock(mp, tableBlock, mp->blockTableBuffer)) return 0;
+
+    uint64_t *data = (uint64_t *) mp->blockTableBuffer;
+    return data[tableIndex];
+}
+
+/* lxfsReadNextBlock(): reads a block and returns the next block in its chain
+ * params: mp - mountpoint
+ * params: block - block number
+ * params: buffer - buffer to read into
+ * returns: next block number, zero on fail
+ */
+
+uint64_t lxfsReadNextBlock(Mountpoint *mp, uint64_t block, void *buffer) {
+    if(lxfsReadBlock(mp, block, buffer)) return 0;
+    return lxfsNextBlock(mp, block);
+}
+
+/* lxfsWriteNextBlock(): writes a block and returns the next block in its chain
+ * params: mp - mountpoint
+ * params: block - block number
+ * params: buffer - buffer to write from
+ * returns: next block number, zero on fail
+ */
+
+uint64_t lxfsWriteNextBlock(Mountpoint *mp, uint64_t block, const void *buffer) {
+    if(lxfsWriteBlock(mp, block, buffer)) return 0;
+    return lxfsNextBlock(mp, block);
+}