Network File Systems (NFS) allow multiple clients to access shared files over a network as if they were stored locally. NFS is widely used in distributed systems to provide seamless file sharing across different machines. The provided code implements core NFS structures, such as nfs_fhandle_t for file handles and nfs_attr_t for file attributes. These structures are essential for managing file metadata and operations in a distributed environment.
The nfs_cache_entry_t structure represents a cached file entry, which includes the file handle, path, attributes, and data. Caching is crucial for improving performance by reducing the number of remote procedure calls (RPCs) to the server. The simulator uses these structures to manage file operations, cache data, and ensure consistency across clients.
The Remote Procedure Call (RPC) framework is the backbone of NFS, enabling clients to execute procedures on remote servers. The nfs_rpc_context_t structure defines the RPC context, including the procedure, version, program, and server address. The nfs_rpc_call function handles the RPC communication, using the clntudp_create function to create a UDP-based RPC client.
typedef struct {
uint32_t procedure;
uint32_t version;
uint32_t program;
struct sockaddr_in server_addr;
int timeout;
} nfs_rpc_context_t;
enum nfs_procedure {
NFS_NULL = 0,
NFS_GETATTR = 1,
NFS_SETATTR = 2,
NFS_LOOKUP = 3,
NFS_READ = 6,
NFS_WRITE = 7,
NFS_CREATE = 8,
NFS_REMOVE = 9,
NFS_RENAME = 11
};
static int nfs_rpc_call(nfs_rpc_context_t *ctx,
void *args,
void *result) {
CLIENT *client;
enum clnt_stat status;
struct timeval tv;
tv.tv_sec = ctx->timeout;
tv.tv_usec = 0;
client = clntudp_create(&ctx->server_addr,
ctx->program,
ctx->version,
tv,
&ctx->socket);
if (!client)
return -ETIMEDOUT;
status = clnt_call(client,
ctx->procedure,
(xdrproc_t)xdr_args,
args,
(xdrproc_t)xdr_result,
result,
tv);
clnt_destroy(client);
return (status == RPC_SUCCESS) ? 0 : -EIO;
}
The nfs_rpc_call function sends an RPC request to the server and waits for the response. If the call succeeds, it returns 0; otherwise, it returns an error code. This framework allows clients to perform file operations, such as reading and writing, by making RPC calls to the server.
File operations, such as reading and writing, are implemented using the nfs_context_t structure, which includes the RPC context and cache. The nfs_read function checks the cache for the requested data before making an RPC call to the server. If the data is not in the cache or is stale, it fetches the data from the server and updates the cache.
typedef struct {
nfs_rpc_context_t *rpc;
nfs_cache_entry_t *cache;
pthread_mutex_t lock;
} nfs_context_t;
static int nfs_read(nfs_context_t *ctx,
nfs_fhandle_t *fh,
void *buffer,
size_t size,
off_t offset) {
struct nfs_read_args args = {
.fh = *fh,
.offset = offset,
.count = size
};
struct nfs_read_res result;
int ret;
pthread_mutex_lock(&ctx->lock);
nfs_cache_entry_t *entry = find_cache_entry(ctx->cache, fh);
if (entry && is_cache_valid(entry)) {
memcpy(buffer, entry->data + offset, size);
update_cache_access(entry);
pthread_mutex_unlock(&ctx->lock);
return size;
}
// Perform RPC call
ret = nfs_rpc_call(ctx->rpc, &args, &result);
if (ret == 0) {
memcpy(buffer, result.data, result.count);
update_cache(ctx->cache, fh, result.data, result.count);
}
pthread_mutex_unlock(&ctx->lock);
return ret == 0 ? result.count : ret;
}
The nfs_write function updates the cache and then sends an RPC call to the server to write the data. This ensures that the cache remains consistent with the server’s data.
static int nfs_write(nfs_context_t *ctx,
nfs_fhandle_t *fh,
const void *buffer,
size_t size,
off_t offset) {
struct nfs_write_args args = {
.fh = *fh,
.offset = offset,
.count = size,
.data = (void *)buffer
};
struct nfs_write_res result;
int ret;
pthread_mutex_lock(&ctx->lock);
// Update cache before write
nfs_cache_entry_t *entry = find_cache_entry(ctx->cache, fh);
if (entry) {
update_cache_data(entry, buffer, offset, size);
entry->dirty = true;
}
ret = nfs_rpc_call(ctx->rpc, &args, &result);
pthread_mutex_unlock(&ctx->lock);
return ret == 0 ? result.count : ret;
}
These functions ensure that file operations are efficient and consistent, leveraging the cache to minimize RPC calls.
Cache management is critical for optimizing NFS performance. The nfs_cache_t structure manages the cache, including the maximum number of entries, maximum size, and current size. The nfs_cache_init function initializes the cache, while the nfs_cache_evict function removes stale or least-recently-used entries when the cache exceeds its limits.
typedef struct {
size_t max_entries;
size_t max_size;
size_t current_size;
struct list_head entries;
pthread_mutex_t lock;
} nfs_cache_t;
static nfs_cache_t* nfs_cache_init(size_t max_entries, size_t max_size) {
nfs_cache_t *cache = malloc(sizeof(nfs_cache_t));
if (!cache)
return NULL;
cache->max_entries = max_entries;
cache->max_size = max_size;
cache->current_size = 0;
INIT_LIST_HEAD(&cache->entries);
pthread_mutex_init(&cache->lock, NULL);
return cache;
}
static void nfs_cache_evict(nfs_cache_t *cache) {
nfs_cache_entry_t *entry, *tmp;
list_for_each_entry_safe(entry, tmp, &cache->entries, cache_list) {
if (cache->current_size <= cache->max_size)
break;
if (entry->dirty)
flush_cache_entry(entry);
cache->current_size -= entry->data_size;
list_del(&entry->cache_list);
free_cache_entry(entry);
}
}
The nfs_cache_add function adds a new entry to the cache, evicting old entries if necessary. This ensures that the cache remains within its size limits while providing fast access to frequently used data.
Consistency is a major challenge in distributed file systems. The nfs_consistency_t structure tracks the version and validity of cached data. The check_consistency function compares the cached data’s modification time with the server’s data to determine if the cache is stale.
typedef struct {
uint64_t version;
struct timespec validity;
bool weak_consistency;
} nfs_consistency_t;
static int check_consistency(nfs_context_t *ctx,
nfs_cache_entry_t *entry) {
struct nfs_getattr_args args = {
.fh = entry->fh
};
struct nfs_getattr_res result;
int ret;
ret = nfs_rpc_call(ctx->rpc, &args, &result);
if (ret)
return ret;
if (result.attr.mtime.tv_sec > entry->attr.mtime.tv_sec) {
// Cache is stale
invalidate_cache_entry(entry);
return -ESTALE;
}
return 0;
}
The update_consistency function updates the cache entry’s version and validity, ensuring that the cache remains consistent with the server’s data.
Security is essential for protecting data in a distributed environment. The nfs_auth_t structure defines the authentication mechanism, including system-based and Kerberos-based authentication. The setup_security function configures the RPC client’s authentication handle based on the specified mechanism.
typedef struct {
uint32_t auth_type;
union {
struct {
uint32_t uid;
uint32_t gid;
uint32_t stamp;
} sys;
struct {
char *principal;
char *instance;
char *realm;
} krb;
} auth;
} nfs_auth_t;
static int setup_security(nfs_context_t *ctx, nfs_auth_t *auth) {
AUTH *auth_handle;
switch (auth->auth_type) {
case AUTH_SYS:
auth_handle = authunix_create(hostname,
auth->auth.sys.uid,
auth->auth.sys.gid,
0, NULL);
break;
case AUTH_KRB:
auth_handle = authkerb_create(auth->auth.krb.principal,
auth->auth.krb.instance,
auth->auth.krb.realm);
break;
default:
return -EINVAL;
}
if (!auth_handle)
return -ENOMEM;
ctx->rpc->client->cl_auth = auth_handle;
return 0;
}
This implementation ensures that only authorized clients can access the file system, protecting sensitive data from unauthorized access.
Error handling is critical for ensuring the reliability of NFS. The nfs_error_t structure defines the error code, message, and retry parameters. The handle_nfs_error function processes errors, such as stale file handles or timeouts, and determines whether the operation should be retried.
typedef struct {
int error_code;
const char *message;
bool retry_allowed;
int retry_count;
int retry_delay;
} nfs_error_t;
static int handle_nfs_error(nfs_context_t *ctx,
nfs_error_t *error) {
switch (error->error_code) {
case ESTALE:
// Handle stale file handle
invalidate_cache(ctx->cache, error->fh);
return -ESTALE;
case ETIMEDOUT:
if (error->retry_allowed &&
error->retry_count < MAX_RETRIES) {
sleep(error->retry_delay);
error->retry_count++;
return 1; // Retry operation
}
break;
case EACCES:
// Handle authentication failure
return refresh_credentials(ctx);
}
return error->error_code;
}
This function ensures that the system can recover from transient errors, improving its reliability and robustness.
Performance optimization is essential for ensuring that NFS meets the demands of modern applications. The nfs_perf_params_t structure defines parameters for read-ahead, write-behind, and concurrent operations. The optimize_read_ahead function prefetches data to reduce latency, while the handle_write_behind function flushes dirty cache entries to the server.
typedef struct {
size_t read_ahead_size;
size_t write_behind_size;
int max_concurrent_ops;
bool async_writes;
} nfs_perf_params_t;
static int optimize_read_ahead(nfs_context_t *ctx,
nfs_fhandle_t *fh,
off_t offset) {
nfs_cache_entry_t *entry;
size_t read_size;
entry = find_cache_entry(ctx->cache, fh);
if (!entry || offset >= entry->attr.size)
return 0;
read_size = min(ctx->params.read_ahead_size,
entry->attr.size - offset);
return prefetch_data(ctx, fh, offset, read_size);
}
static int handle_write_behind(nfs_context_t *ctx) {
nfs_cache_entry_t *entry, *tmp;
int ret = 0;
list_for_each_entry_safe(entry, tmp, &ctx->cache->entries, cache_list) {
if (entry->dirty) {
ret = flush_cache_entry(entry);
if (ret)
break;
}
}
return ret;
}
These optimizations ensure that NFS delivers high performance, even under heavy workloads.
The monitoring system tracks key performance metrics, such as read/write operations, cache hits/misses, and RPC calls. The nfs_stats_t structure stores these metrics, and the update_stats function updates them during file operations. The print_stats function displays the metrics, providing insights into the system’s performance.
typedef struct {
uint64_t read_ops;
uint64_t write_ops;
uint64_t cache_hits;
uint64_t cache_misses;
uint64_t rpc_calls;
uint64_t rpc_retries;
struct timespec uptime;
} nfs_stats_t;
static void update_stats(nfs_context_t *ctx,
enum nfs_stat_type type) {
pthread_mutex_lock(&ctx->stats_lock);
switch (type) {
case STAT_READ:
ctx->stats.read_ops++;
break;
case STAT_WRITE:
ctx->stats.write_ops++;
break;
case STAT_CACHE_HIT:
ctx->stats.cache_hits++;
break;
case STAT_CACHE_MISS:
ctx->stats.cache_misses++;
break;
case STAT_RPC:
ctx->stats.rpc_calls++;
break;
}
pthread_mutex_unlock(&ctx->stats_lock);
}
static void print_stats(nfs_context_t *ctx) {
nfs_stats_t stats;
pthread_mutex_lock(&ctx->stats_lock);
memcpy(&stats, &ctx->stats, sizeof(stats));
pthread_mutex_unlock(&ctx->stats_lock);
printf("NFS Statistics:\n");
printf("Read Operations: %lu\n", stats.read_ops);
printf("Write Operations: %lu\n", stats.write_ops);
printf("Cache Hit Ratio: %.2f%%\n",
(float)stats.cache_hits / (stats.cache_hits + stats.cache_misses) * 100);
printf("RPC Calls: %lu\n", stats.rpc_calls);
printf("RPC Retries: %lu\n", stats.rpc_retries);
}
This monitoring system helps administrators identify performance bottlenecks and optimize the system.
The implementation of a Network File System requires careful attention to RPC communication, caching strategies, consistency protocols, and security mechanisms. The provided code demonstrates key components necessary for a robust NFS implementation, including file operations, cache management, and performance optimization. By carefully designing and implementing these mechanisms, developers can create efficient and secure distributed file systems.