Readme and Changelog

  - Improves RPC stability

  - Removes manual updates to Mercury public IDs from Hermes-Mercury to Margo

- Updated Spack to support the latest version ([!190](https://storage.bsc.es/gitlab/hpc/gekkofs/-/merge_request/190)).

- Rewrite of the resolve path function to improve performance by making the

    use of syscall for following symlinks optional

    ([!183](https://storage.bsc.es/gitlab/hpc/gekkofs/-/merge_requests/183)).

### Removed

### New

- Rewrite of the resolve path function to improve performance by making the

  use of syscall for following symlinks optional

  ([!183](https://storage.bsc.es/gitlab/hpc/gekkofs/-/merge_requests/183)).

- Support for client-side per process logging, activated

  with `LIBGKFS_LOG_PER_PROCESS` ([!179](https://storage.bsc.es/gitlab/hpc/gekkofs/-/merge_requests/179)).

- Support mtime with option gkfs::config::metadata::

* [gkfs] Shutdown time: 1.032 seconds

```

## All CMake options

#### Core

- `GKFS_BUILD_TOOLS` - Build tools (default: OFF)

- `GKFS_BUILD_TESTS` - Build tests (default: OFF)

- `GKFS_CREATE_CHECK_PARENTS` - Enable checking parent directory for existence before creating children (default: ON)

- `GKFS_MAX_INTERNAL_FDS` - Number of file descriptors reserved for internal use (default: 256)

- `GKFS_MAX_OPEN_FDS` - Maximum number of open file descriptors supported (default: 1024)

- `GKFS_RENAME_SUPPORT` - Enable support for rename (default: OFF)

- `GKFS_SYMLINK_SUPPORT` - Enable support for symlinks (default: ON)

- `GKFS_FOLLOW_EXTERNAL_SYMLINKS` - Enable support for following external links for resolving the path (default: OFF)

- `GKFS_USE_LEGACY_PATH_RESOLVE` - Use the legacy implementation of the resolve function, deprecated (default: OFF)

- `GKFS_USE_GUIDED_DISTRIBUTION` - Use guided data distributor (default: OFF)

- `GKFS_USE_GUIDED_DISTRIBUTION_PATH` - File Path for guided distributor (default: /tmp/guided.txt)

#### Logging

- `GKFS_ENABLE_CLIENT_LOG` - Enable logging messages in clients (default: ON)

- `GKFS_CLIENT_LOG_MESSAGE_SIZE` - Maximum size of a log message in the client library (default: 1024)

#### Statistics

- `GKFS_ENABLE_PROMETHEUS` - Enable pushing daemon statistics to a Prometheus Gateway (default: OFF)

- `GKFS_ENABLE_CLIENT_METRICS` - Enable client metrics via MSGPack (default: OFF)

#### Backends

- `GKFS_ENABLE_ROCKSDB` - Enable RocksDB metadata backend (default: ON)

- `GKFS_ENABLE_PARALLAX` - Enable Parallax metadata support (default: OFF)

## All environment variables

The GekkoFS daemon, client, and proxy support a number of environment variables to augment its functionality:

### Client

#### Core

- `LIBGKFS_HOSTS_FILE` - Path to the hostsfile (created by the daemon and mandatory for the client).

#### Logging

- `LIBGKFS_LOG` - Log module of the client. 

Available modules are: `none`, `syscalls`, `syscalls_at_entry`, `info`, `critical`, `errors`, `warnings`, `mercury`, `debug`, `most`, `all`, `trace_reads`, `help`.

- `LIBGKFS_LOG_OUTPUT` - Path to the log file of the client.

- `LIBGKFS_LOG_PER_PROCESS` - Write separate logs per client process.

- `LIBGKFS_LOG_SYSCALL_FILTER` - Filter out specific system calls from log messages.

- `LIBGKFS_LOG_OUTPUT_TRUNC` - Truncate the file used for logging.

#### Client-metrics

Client-metrics require the CMake argument `-DGKFS_ENABLE_CLIENT_METRICS=ON` (see above).

- `LIBGKFS_ENABLE_METRICS` - Enable capturing client-side metrics.

- `LIBGKFS_METRICS_FLUSH_INTERVAL` - Set the flush interval for client metrics.

- `LIBGKFS_METRICS_PATH` - Path to flush client metrics.

- `LIBGKFS_METRICS_IP_PORT` - Enable flushing to a set ZeroMQ server (replaces `LIBGKFS_METRICS_PATH`).

- `LIBGKFS_PROXY_PID_FILE` - Path to the proxy pid file (when using the GekkoFS proxy).

- `LIBGKFS_NUM_REPL` - Number of replicas for data.

### Daemon

#### Logging

- `GKFS_DAEMON_LOG_PATH` - Path to the log file of the daemon.

- `GKFS_DAEMON_LOG_LEVEL` - Log level of the daemon. Available levels are: `off`, `critical`, `err`, `warn`, `info`, `debug`, `trace`.

### Proxy

#### Logging

- `GKFS_PROXY_LOG_PATH` - Path to the log file of the proxy.

- `GKFS_PROXY_LOG_LEVEL` - Log level of the proxy. Available levels are: `off`, `critical`, `err`, `warn`, `info`, `debug`, `trace`.

## Acknowledgment

This software was partially supported by the EC H2020 funded NEXTGenIO project (Project ID: 671951, www.nextgenio.eu).