advaced unix programing

#include "apue.h" #include "apue_db.h" #include <fcntl.h> /* open & db_open flags */ #include <stdarg.h> #include <errno.h> #include <sys/uio.h> /* struct iovec */ /* * Internal index file constants. * These are used to construct records in the * index file and data file. */ #define IDXLEN_SZ 4 /* index record length (ASCII chars) */ #define SEP ':' /* separator char in index record */ #define SPACE ' ' /* space character */ #define NEWLINE '\n' /* newline character */ /* * The following definitions are for hash chains and free * list chain in the index file. */ #define PTR_SZ 6 /* size of ptr field in hash chain */ #define PTR_MAX 999999 /* max file offset = 10**PTR_SZ - 1 */ #define NHASH_DEF 137 /* default hash table size */ #define FREE_OFF 0 /* free list offset in index file */ #define HASH_OFF PTR_SZ /* hash table offset in index file */ typedef unsigned long DBHASH; /* hash values */ typedef unsigned long COUNT; /* unsigned counter */ /* * Library's private representation of the database. */ typedef struct { int idxfd; /* fd for index file */ int datfd; /* fd for data file */ char *idxbuf; /* malloc'ed buffer for index record */ char *datbuf; /* malloc'ed buffer for data record*/ char *name; /* name db was opened under */ off_t idxoff; /* offset in index file of index record */ /* key is at (idxoff + PTR_SZ + IDXLEN_SZ) */ size_t idxlen; /* length of index record */ /* excludes IDXLEN_SZ bytes at front of record */ /* includes newline at end of index record */ off_t datoff; /* offset in data file of data record */ size_t datlen; /* length of data record */ /* includes newline at end */ off_t ptrval; /* contents of chain ptr in index record */ off_t ptroff; /* chain ptr offset pointing to this idx record */ off_t chainoff; /* offset of hash chain for this index record */ off_t hashoff; /* offset in index file of hash table */ DBHASH nhash; /* current hash table size */ COUNT cnt_delok; /* delete OK */ COUNT cnt_delerr; /* delete error */ COUNT cnt_fetchok; /* fetch OK */ COUNT cnt_fetcherr; /* fetch error */ COUNT cnt_nextrec; /* nextrec */ COUNT cnt_stor1; /* store: DB_INSERT, no empty, appended */ COUNT cnt_stor2; /* store: DB_INSERT, found empty, reused */ COUNT cnt_stor3; /* store: DB_REPLACE, diff len, appended */ COUNT cnt_stor4; /* store: DB_REPLACE, same len, overwrote */ COUNT cnt_storerr; /* store error */ } DB; /* * Internal functions. */ static DB *_db_alloc(int); static void _db_dodelete(DB *); static int _db_find_and_lock(DB *, const char *, int); static int _db_findfree(DB *, int, int); static void _db_free(DB *); static DBHASH _db_hash(DB *, const char *); static char *_db_readdat(DB *); static off_t _db_readidx(DB *, off_t); static off_t _db_readptr(DB *, off_t); static void _db_writedat(DB *, const char *, off_t, int); static void _db_writeidx(DB *, const char *, off_t, int, off_t); static void _db_writeptr(DB *, off_t, off_t); /* * Open or create a database. Same arguments as open(2). */ DBHANDLE db_open(const char *pathname, int oflag, ...) { DB *db; int len, mode; size_t i; char asciiptr[PTR_SZ + 1], hash[(NHASH_DEF + 1) * PTR_SZ + 2]; /* +2 for newline and null */ struct stat statbuff; /* * Allocate a DB structure, and the buffers it needs. */ len = strlen(pathname); if ((db = _db_alloc(len)) == NULL) err_dump("db_open: _db_alloc error for DB"); db->nhash = NHASH_DEF;/* hash table size */ db->hashoff = HASH_OFF; /* offset in index file of hash table */ strcpy(db->name, pathname); strcat(db->name, ".idx"); if (oflag & O_CREAT) { va_list ap; va_start(ap, oflag); mode = va_arg(ap, int); va_end(ap); /* * Open index file and data file. */ db->idxfd = open(db->name, oflag, mode); strcpy(db->name + len, ".dat"); db->datfd = open(db->name, oflag, mode); } else { /* * Open index file and data file. */ db->idxfd = open(db->name, oflag); strcpy(db->name + len, ".dat"); db->datfd = open(db->name, oflag); } if (db->idxfd < 0 || db->datfd < 0) { _db_free(db); return(NULL); } if ((oflag & (O_CREAT | O_TRUNC)) == (O_CREAT | O_TRUNC)) { /* * If the database was created, we have to initialize * it. Write lock the entire file so that we can stat * it, check its size, and initialize it, atomically. */ if (writew_lock(db->idxfd, 0, SEEK_SET, 0) < 0) err_dump("db_open: writew_lock error"); if (fstat(db->idxfd, &statbuff) < 0) err_sys("db_open: fstat error"); if (statbuff.st_size == 0) { /* * We have to build a list of (NHASH_DEF + 1) chain * ptrs with a value of 0. The +1 is for the free * list pointer that precedes the hash table. */ sprintf(asciiptr, "%*d", PTR_SZ, 0); hash[0] = 0; for (i = 0; i < NHASH_DEF + 1; i++) strcat(hash, asciiptr); strcat(hash, "\n"); i = strlen(hash); if (write(db->idxfd, hash, i) != i) err_dump("db_open: index file init write error"); } if (un_lock(db->idxfd, 0, SEEK_SET, 0) < 0) err_dump("db_open: un_lock error"); } db_rewind(db); return(db); } /* * Allocate & initialize a DB structure and its buffers. */ static DB * _db_alloc(int namelen) { DB *db; /* * Use calloc, to initialize the structure to zero. */ if ((db = calloc(1, sizeof(DB))) == NULL) err_dump("_db_alloc: calloc error for DB"); db->idxfd = db->datfd = -1; /* descriptors */ /* * Allocate room for the name. * +5 for ".idx" or ".dat" plus null at end. */ if ((db->name = malloc(namelen + 5)) == NULL) err_dump("_db_alloc: malloc error for name"); /* * Allocate an index buffer and a data buffer. * +2 for newline and null at end. */ if ((db->idxbuf = malloc(IDXLEN_MAX + 2)) == NULL) err_dump("_db_alloc: malloc error for index buffer"); if ((db->datbuf = malloc(DATLEN_MAX + 2)) == NULL) err_dump("_db_alloc: malloc error for data buffer"); return(db); } /* * Relinquish access to the database. */ void db_close(DBHANDLE h) { _db_free((DB *)h); /* closes fds, free buffers & struct */ } /* * Free up a DB structure, and all the malloc'ed buffers it * may point to. Also close the file descriptors if still open. */ static void _db_free(DB *db) { if (db->idxfd >= 0) close(db->idxfd); if (db->datfd >= 0) close(db->datfd); if (db->idxbuf != NULL) free(db->idxbuf); if (db->datbuf != NULL) free(db->datbuf); if (db->name != NULL) free(db->name); free(db); } /* * Fetch a record. Return a pointer to the null-terminated data. */ char * db_fetch(DBHANDLE h, const char *key) { DB *db = h; char *ptr; if (_db_find_and_lock(db, key, 0) < 0) { ptr = NULL; /* error, record not found */ db->cnt_fetcherr++; } else { ptr = _db_readdat(db); /* return pointer to data */ db->cnt_fetchok++; } /* * Unlock the hash chain that _db_find_and_lock locked. */ if (un_lock(db->idxfd, db->chainoff, SEEK_SET, 1) < 0) err_dump("db_fetch: un_lock error"); return(ptr); } /* * Find the specified record. Called by db_delete, db_fetch, * and db_store. Returns with the hash chain locked. */ static int _db_find_and_lock(DB *db, const char *key, int writelock) { off_t offset, nextoffset; /* * Calculate the hash value for this key, then calculate the * byte offset of corresponding chain ptr in hash table. * This is where our search starts. First we calculate the * offset in the hash table for this key. */ db->chainoff = (_db_hash(db, key) * PTR_SZ) + db->hashoff; db->ptroff = db->chainoff; /* * We lock the hash chain here. The caller must unlock it * when done. Note we lock and unlock only the first byte. */ if (writelock) { if (writew_lock(db->idxfd, db->chainoff, SEEK_SET, 1) < 0) err_dump("_db_find_and_lock: writew_lock error"); } else { if (readw_lock(db->idxfd, db->chai