## 1. Failure in running the KV store on the LiteOS Cortex-A kernel \(Hi3516 or Hi3518\) due to incorrect path setting for the KV store<a name="section2041345718513"></a>
**Problem**
When the LiteOS Cortex-A kernel \(Hi3516 or Hi3518 platform\) directly calls the API provided by the KV store, the compiled executable program fails to run.
**Possible Causes**
The compiled executable program is run directly without being converted to an application using **AbilityKit** APIs. In this case, the Bundle Manager Service \(BMS\) cannot correctly set the path for storing application data during application installation. As a result, the KV store fails to run.
**Solution**
Call the **UtilsSetEnv** function of the KV store to set the data storage path.
<tbody><trid="row671818445506"><tdclass="cellrowborder"valign="top"width="45.540000000000006%"headers="mcps1.2.3.1.1 "><pid="p871814441501"><aname="p871814441501"></a><aname="p871814441501"></a>int UtilsFileOpen(const char* path, int oflag, int mode)</p>
</td>
<tdclass="cellrowborder"valign="top"width="54.459999999999994%"headers="mcps1.2.3.1.2 "><pid="p127181444165016"><aname="p127181444165016"></a><aname="p127181444165016"></a>Opens or creates a file.</p>
<tdclass="cellrowborder"valign="top"width="54.459999999999994%"headers="mcps1.2.3.1.2 "><pid="p1071884416504"><aname="p1071884416504"></a><aname="p1071884416504"></a>Closes a file with a specified file descriptor.</p>
</td>
</tr>
<trid="row6718744105017"><tdclass="cellrowborder"valign="top"width="45.540000000000006%"headers="mcps1.2.3.1.1 "><pid="p137181644145015"><aname="p137181644145015"></a><aname="p137181644145015"></a>int UtilsFileRead(int fd, char *buf, unsigned int len)</p>
</td>
<tdclass="cellrowborder"valign="top"width="54.459999999999994%"headers="mcps1.2.3.1.2 "><pid="p1171854410509"><aname="p1171854410509"></a><aname="p1171854410509"></a>Reads a specified length of data from a file with the specified file descriptor and writes the data into the buffer.</p>
</td>
</tr>
<trid="row2071817440509"><tdclass="cellrowborder"valign="top"width="45.540000000000006%"headers="mcps1.2.3.1.1 "><pid="p17718144465012"><aname="p17718144465012"></a><aname="p17718144465012"></a>int UtilsFileWrite(int fd, const char *buf, unsigned int len)</p>
</td>
<tdclass="cellrowborder"valign="top"width="54.459999999999994%"headers="mcps1.2.3.1.2 "><pid="p67191444145012"><aname="p67191444145012"></a><aname="p67191444145012"></a>Writes a specified length of data into a file with the specified file descriptor.</p>
<tdclass="cellrowborder"valign="top"width="54.459999999999994%"headers="mcps1.2.3.1.2 "><pid="p2071919446507"><aname="p2071919446507"></a><aname="p2071919446507"></a>Deletes a specified file.</p>
</td>
</tr>
<trid="row1071964425013"><tdclass="cellrowborder"valign="top"width="45.540000000000006%"headers="mcps1.2.3.1.1 "><pid="p20719114405010"><aname="p20719114405010"></a><aname="p20719114405010"></a>int UtilsFileStat(const char *path, unsigned int *fileSize)</p>
</td>
<tdclass="cellrowborder"valign="top"width="54.459999999999994%"headers="mcps1.2.3.1.2 "><pid="p8719144435015"><aname="p8719144435015"></a><aname="p8719144435015"></a>Obtains the file size.</p>
</td>
</tr>
<trid="row2071924417504"><tdclass="cellrowborder"valign="top"width="45.540000000000006%"headers="mcps1.2.3.1.1 "><pid="p57193447501"><aname="p57193447501"></a><aname="p57193447501"></a>int UtilsFileSeek(int fd, int offset, unsigned int whence)</p>
</td>
<tdclass="cellrowborder"valign="top"width="54.459999999999994%"headers="mcps1.2.3.1.2 "><pid="p1071934495014"><aname="p1071934495014"></a><aname="p1071934495014"></a>Adjusts the read and write position offset in a file.</p>
<tdclass="cellrowborder"valign="top"width="54.459999999999994%"headers="mcps1.2.3.1.2 "><pid="p113501041155511"><aname="p113501041155511"></a><aname="p113501041155511"></a>Copies the source file to a target file.</p>
<tdclass="cellrowborder"valign="top"width="54.459999999999994%"headers="mcps1.2.3.1.2 "><pid="p921744595517"><aname="p921744595517"></a><aname="p921744595517"></a>Moves the source file into a target file.</p>
<tbody><trid="row34145016535"><tdclass="cellrowborder"valign="top"width="57.38999999999999%"headers="mcps1.2.3.1.1 "><pid="p980953910190"><aname="p980953910190"></a><aname="p980953910190"></a>int UtilsGetValue(const char* key, char* value, unsigned int len)</p>
</td>
<tdclass="cellrowborder"valign="top"width="42.61%"headers="mcps1.2.3.1.2 "><pid="p13562171015712"><aname="p13562171015712"></a><aname="p13562171015712"></a>Obtains the value matching a specified key from the file system or cache.</p>
<tdclass="cellrowborder"valign="top"width="42.61%"headers="mcps1.2.3.1.2 "><pid="p2431455765"><aname="p2431455765"></a><aname="p2431455765"></a>Adds or updates the value matching a specified key in the file system or cache.</p>
<tdclass="cellrowborder"valign="top"width="42.61%"headers="mcps1.2.3.1.2 "><pid="p126575774517"><aname="p126575774517"></a><aname="p126575774517"></a>Deletes the value matching a specified key from the file system or cache.</p>
</td>
</tr>
</tbody>
</table>
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<a name="section17450172710292"></a>
### Developing a Native Application for the KV Store That Uses the LiteOS Cortex-A Kernel \(Hi3516 or Hi3518\)<a name="section258354119295"></a>
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);
- 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.
The Utils library stores common basic components of OpenHarmony. These basic components can be used by OpenHarmony service subsystems and upper-layer applications.
The Utils library provides the following capabilities on different platforms:
LiteOS Cortex-M \(Hi3861 platform\): KV store, file operations, IoT peripheral control, and system attribute dumping
LiteOS Cortex-A \(Hi3516 or Hi3518 platform\): KV store, timer, JavaScript APIs for data and file storage, and system attribute dumping
