If software application project fails to compile because files from xyl_oslib or fat_fs library could not be found, that means that during the BSP compilation stage these libraries were not considered. Most likely the problem is that these libraries were not properly included or were not included at all to the BSP.
When a BSP is created and associated to the hardware design, the SDK tool will make different Xilinx libraries available by default, as well as the drivers for all the IPs included in the referenced design. At first, xyl_oslib and fat_fs libraries will not be included, while some generic (actually non-existing) driver will be assigned for logicBRICKS IPs. If Board Support Package Settings window is opened, the list of available libraries from Xilinx can be seen and selected according to application requiremants. Default CPU driver (latest available version for the tool build) will be automatically assigned.
In order to make other libraries visible, such as xyl_oslib and fat_fs, as well as drivers, a correct path in Xilinx Tools->Repositories window should be set. It is recommended to have drivers folder (the one containing logicBRICKS IPs' driver) and sw_services folder (the one containing xyl_oslib and fat_fs libraries) both in the same folder. For example, let's name this folder hardware. Usually, the hardware folder also contains pcores folder, where logicBRICKS IPs are located, hence the name of the folder. To get all the necessary items included in softawre application project in SDK tool (drivers and libraries), the hardware folder should be added to the Local Repositories window by clicking the New button. Relative and absolute paths are accaptable.
Apply button and then Rescan button should be clicked before final confirmation with the OK button. If BSP Settings window is opened at this point, xyl_oslib and fat_fs libraries will both be listed, and thus available for selection. In the drivers menu of the Settings window, the drivers for logicBRICKS IPs are automatically assigned. If this is not the case, the logicBRICKS driver can be selected from the dropbox menu for each of the IPs. Now, all the necessary libraries and drivers should have been properly assigned for the BSP.