# Utils Development
## Available APIs
**Table 1** APIs for file operations
| Function | Description |
| ---------- | ------------- |
| int UtilsFileOpen(const char* path, int oflag, int mode) | Opens or creates a file. |
| int UtilsFileClose(int fd) | Closes a file with a specified file descriptor. |
| int UtilsFileRead(int fd, char *buf, unsigned int len) | Reads a specified length of data from a file with the specified file descriptor and writes the data into the buffer. |
| int UtilsFileWrite(int fd, const char *buf, unsigned int len) | Writes a specified length of data into a file with the specified file descriptor. |
| int UtilsFileDelete(const char *path) | Deletes a specified file. |
| int UtilsFileStat(const char *path, unsigned int *fileSize) | Obtains the file size. |
| int UtilsFileSeek(int fd, int offset, unsigned int whence) | Adjusts the read and write position offset in a file. |
| int UtilsFileCopy(const char* src, const char* dest) | Copies the source file to a target file. |
| int UtilsFileMove(const char* src, const char* dest) | Moves the source file into a target file. |
Sample code for file operations:
```
// Open a file and write data.
char fileName[] = "testfile";
static const char def[] = "utils_file_operation implement.";
int fd = UtilsFileOpen(fileName, O_RDWR_FS | O_CREAT_FS | O_TRUNC_FS, 0);
printf("file handle = %d\n", fd);
int ret = UtilsFileWrite(fd, def, strlen(def));
printf("write ret = %d\n", ret);
// Adjust the position offset in the file.
ret = UtilsFileSeek(fd, 5, SEEK_SET_FS);
printf("lseek ret = %d\n", ret);
// Read data and close the file.
char buf[64] = {0};
int readLen = UtilsFileRead(fd, buf, 64);
ret = UtilsFileClose(fd);
printf("read len = %d : buf = %s\n", readLen, buf);
// Obtain the file size.
int fileLen = 0;
ret = UtilsFileStat(fileName, &fileLen);
printf("file size = %d\n", fileLen);
// Delete the file.
ret = UtilsFileDelete(fileName);
printf("delete ret = %d\n", ret);
```
**Table 2** APIs for KV store operations
| Function | Description |
| ----------- | ---------------- |
| int UtilsGetValue(const char* key, char* value, unsigned int len) | Obtains the value matching a specified key from the file system or cache. |
| int UtilsSetValue(const char* key, const char* value) | Adds or updates the value matching a specified key in the file system or cache. |
| int UtilsDeleteValue(const char* key) | Deletes the value matching a specified key from the file system or cache. |
Sample code for the KV store:
```
// Set the value matching the specified key.
char key[] = "rw.sys.version_100";
char value[] = "Hello kv operation implement!";
int ret = UtilsSetValue(key, value);
printf("UtilsSetValue set ret = %d\n", ret);
// Obtain the value matching the specified key.
char temp[128] = {0};
ret = UtilsGetValue(key, temp, 128);
printf("UtilsGetValue get ret = %d, temp = %s\n", ret, temp);
// Delete the value matching the specified key.
ret = UtilsDeleteValue(key);
printf("UtilsDeleteValue delete ret = %d\n", ret);
```
## How to Develop
### Developing a Native Application for the KV Store That Uses the LiteOS Cortex-A Kernel \(Hi3516 or Hi3518\)
1. Develop the native application for the KV store using **AbilityKit** APIs.
- Write the user program by calling the APIs provided by the KV store and compile the **libLauncher.so** file.
```
// Set the value matching the specified key.
char key[] = "rw.sys.version_100";
char value[] = "Hello kv operation implement!";
int ret = UtilsSetValue(key, value);
printf("UtilsSetValue set ret = %d\n", ret);
// Obtain the value matching the specified key.
char temp[128] = {0};
ret = UtilsGetValue(key, temp, 128);
printf("UtilsGetValue get ret = %d, temp = %s\n", ret, temp);
// Delete the value matching the specified key.
ret = UtilsDeleteValue(key);
printf("UtilsDeleteValue delete ret = %d\n", ret);
```
- Edit the **config.json** file as follows:
```
{
"app": {
"bundleName": "com.example.launcher",
"vendor": "example,
"version": {
"code": 1,
"name": "1.0"
}
},
"deviceConfig": {
"default": {
"reqSdk": {
"compatible": "zsdk 1.0.0",
"target": "zsdk 1.0.1"
},
"keepAlive": false
},
"smartCamera": {
"reqSdk": {
"compatible": "zsdk 1.0.0",
"target": "zsdk 1.0.1"
},
"keepAlive": false
}
},
"module": {
"package": "com.example.launcher",
"name": ".MyHarmonyAbilityPackage",
"deviceType": [
"phone", "tv","tablet", "pc","car","smartWatch","sportsWatch","smartCamera"
],
"distro": {
"deliveryWithInstall": true,
"moduleName": "Launcher",
"moduleType": "entry"
},
"abilities": [{
"name": "MainAbility",
"icon": "res/drawable/phone.png",
"label": "test app 1",
"launchType": "standard",
"type": "page"
},
{
"name": "SecondAbility",
"icon": "res/drawable/phone.png",
"label": "test app 2",
"launchType": "standard",
"type": "page"
},
{
"name": "ServiceAbility",
"icon": "res/drawable/phone.png",
"label": "test app 2",
"launchType": "standard",
"type": "service"
}
]
}
}
```
- Generate a HAP file.
- Add resource files in the **res/drawable** directory based on the following directory structure.
- Compress the **libLauncher.so**, **config.json**, and resource files into a ZIP package and change the file name extension to **.hap**, for example, **Launcher.hap**.
2. Connect the development board and send the command for installing the native KV store application to the board through the serial port.
```
./nfs/dev_tools/bin/bm install -p /nfs/Launcher.hap
```
3. Send the command for running the native KV store application to the board through the serial port.
```
./nfs/dev_tools/bin/aa start -p com.example.launcher -n ServiceAbility
```
### Dumping System Attributes on the Platform That Uses the LiteOS Cortex-M Kernel
1. Connect the development board and send the **AT+SYSPARA** command to the board through the serial port.
```
AT+SYSPARA
```
**Figure 1** Output of the system attribute dumping command for the LiteOS Cortex-M kernel
### Dumping System Attributes on the Platform That Uses the LiteOS Cortex-A Kernel
1. Connect the development board and run the **os\_dump --help** command in the **bin** directory to view the **os\_dump** help information.
```
./bin/os_dump --help
```
2. Run the **os\_dump -l** command in the **bin** directory to view system modules that support attribute dumping.
```
./bin/os_dump -l
```
3. Run the **os\_dump syspara** command in the **bin** directory to dump the current system attributes.
```
./bin/os_dump syspara
```
**Figure 2** Output of the system attribute dumping command for the LiteOS Cortex-A kernel
