Add lesson 2

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+In the last lesson to build our app we've included its *.inf file as a component to the other package and have built this package. It is clearly not a good solution and in this lesson we will create our own package.
+
+First lets remove our app from the `OvmfPkg/OvmfPkgX64.dsc` file:
+```
+ ################################################################################
+ [Components]
+-  SimplestApp/SimplestApp.inf
+   OvmfPkg/ResetVector/ResetVector.inf
+
+```
+
+Then create `UefiLessonsPkg` folder in the edk2 directory and move our app into this folder:
+```
+mkdir UefiLessonsPkg
+mv SimplestApp UefiLessonsPkg/SimplestApp
+```
+
+Then we need to create platform description file (DSC) for our newly created package:
+```
+$ vi UefiLessonsPkg/UefiLessonsPkg.dsc
+[Defines]
+  PLATFORM_NAME                  = UefiLessonsPkg
+  PLATFORM_GUID                  = 3db7270f-ffac-4139-90a4-0ae68f3f8167
+  PLATFORM_VERSION               = 0.01
+  DSC_SPECIFICATION              = 0x00010006
+  OUTPUT_DIRECTORY               = Build/UefiLessonsPkg
+  SUPPORTED_ARCHITECTURES        = X64
+  BUILD_TARGETS                  = RELEASE
+  SKUID_IDENTIFIER               = DEFAULT
+
+[Components]
+  UefiLessonsPkg/SimplestApp/SimplestApp.inf
+```
+Full specification for the Platform Description (DSC) File can be found under https://edk2-docs.gitbook.io/edk-ii-dsc-specification/
+
+Let's try to build our SimplestApp module that is now in our own package:
+```
+$ . edksetup.sh
+$ build --platform=UefiLessonsPkg/UefiLessonsPkg.dsc \
+        --module=UefiLessonsPkg/SimplestApp/SimplestApp.inf \
+        --arch=X64 \
+        --buildtarget=RELEASE \
+        --tagname=GCC5
+```
+
+Unfortunately the build would fail:
+```
+build.py...
+/home/kostr/edk2/UefiLessonsPkg/UefiLessonsPkg.dsc(...): error 4000: Instance of library class [UefiApplicationEntryPoint] is not found
+        in [/home/kostr/edk2/UefiLessonsPkg/SimplestApp/SimplestApp.inf] [X64]
+        consumed by module [/home/kostr/edk2/UefiLessonsPkg/SimplestApp/SimplestApp.inf]
+```
+
+To fix this we need to add `UefiApplicationEntryPoint` to the `LibraryClasses` section in our `UefiLessonsPkg.dsc` file.
+To find necessay include lets search our edk2 codebase:
+```
+$ grep UefiApplicationEntryPoint -r ./ --include=*.inf | grep LIBRARY_CLASS
+./MdePkg/Library/UefiApplicationEntryPoint/UefiApplicationEntryPoint.inf:  LIBRARY_CLASS                  = UefiApplicationEntryPoint|UEFI_APPLICATION
+```
+
+Therefore we need to add this strings to our *.dsc file:
+```
+[LibraryClasses]
+  UefiApplicationEntryPoint|MdePkg/Library/UefiApplicationEntryPoint/UefiApplicationEntryPoint.inf
+```
+
+Let's try to rebuild:
+```
+$ build --platform=UefiLessonsPkg/UefiLessonsPkg.dsc \
+        --module=UefiLessonsPkg/SimplestApp/SimplestApp.inf \
+        --arch=X64 \
+        --buildtarget=RELEASE \
+        --tagname=GCC5
+```
+
+But the build would fail again:
+```
+build.py...
+/home/kostr/tiano/edk2/UefiLessonsPkg/UefiLessonsPkg.dsc(...): error 4000: Instance of library class [UefiBootServicesTableLib] is not found
+        in [/home/kostr/tiano/edk2/MdePkg/Library/UefiApplicationEntryPoint/UefiApplicationEntryPoint.inf] [X64]
+        consumed by module [/home/kostr/tiano/edk2/UefiLessonsPkg/SimplestApp/SimplestApp.inf]
+```
+
+As we see the error message is the same. It seems like `UefiApplicationEntryPoint` module that we've included needs some additional includes. So we search necessary libraries again... and again... and again.
+In the end our *.dsc file would be looking like this:
+```
+[Defines]
+  PLATFORM_NAME                  = UefiLessonsPkg
+  PLATFORM_GUID                  = 3db7270f-ffac-4139-90a4-0ae68f3f8167
+  PLATFORM_VERSION               = 0.01
+  DSC_SPECIFICATION              = 0x00010006
+  OUTPUT_DIRECTORY               = Build/UefiLessonsPkg
+  SUPPORTED_ARCHITECTURES        = X64
+  BUILD_TARGETS                  = RELEASE
+  SKUID_IDENTIFIER               = DEFAULT
+
+[LibraryClasses]
+  UefiApplicationEntryPoint|MdePkg/Library/UefiApplicationEntryPoint/UefiApplicationEntryPoint.inf
+  UefiBootServicesTableLib|MdePkg/Library/UefiBootServicesTableLib/UefiBootServicesTableLib.inf
+  DebugLib|MdePkg/Library/UefiDebugLibConOut/UefiDebugLibConOut.inf
+  BaseLib|MdePkg/Library/BaseLib/BaseLib.inf
+  PcdLib|MdePkg/Library/BasePcdLibNull/BasePcdLibNull.inf
+  BaseMemoryLib|MdePkg/Library/BaseMemoryLib/BaseMemoryLib.inf
+  RegisterFilterLib|MdePkg/Library/RegisterFilterLibNull/RegisterFilterLibNull.inf
+  PrintLib|MdePkg/Library/BasePrintLib/BasePrintLib.inf
+  DebugPrintErrorLevelLib|MdePkg/Library/BaseDebugPrintErrorLevelLib/BaseDebugPrintErrorLevelLib.inf
+
+[Components]
+  UefiLessonsPkg/SimplestApp/SimplestApp.inf
+```
+
+After the successful build the result binary would be in a `Build/UefiLessonsPkg/RELEASE_GCC5/X64` folder:
+```
+$ ls -lh Build/UefiLessonsPkg/RELEASE_GCC5/X64/SimplestApp.efi
+-rw-r--r-- 1 kostr kostr 960 Jun 13 12:47 Build/UefiLessonsPkg/RELEASE_GCC5/X64/SimplestApp.efi
+```
+
+Let's copy in our `UEFI_disk` folder and run it in OVMF:
+```
+$ cp Build/UefiLessonsPkg/RELEASE_GCC5/X64/SimplestApp.efi ~/UEFI_disk/
+$ qemu-system-x86_64 -drive if=pflash,format=raw,file=Build/OvmfX64/RELEASE_GCC5/FV/OVMF.fd \
+                     -drive format=raw,file=fat:rw:~/UEFI_disk \
+                     -nographic \
+                     -net none
+```
+
+Hopefully everything would be the same it was earlier:
+```
+UEFI Interactive Shell v2.2
+EDK II
+UEFI v2.70 (EDK II, 0x00010000)
+Mapping table
+      FS0: Alias(s):HD0a1:;BLK1:
+          PciRoot(0x0)/Pci(0x1,0x1)/Ata(0x0)/HD(1,MBR,0xBE1AFDFA,0x3F,0xFBFC1)
+     BLK0: Alias(s):
+          PciRoot(0x0)/Pci(0x1,0x1)/Ata(0x0)
+     BLK2: Alias(s):
+          PciRoot(0x0)/Pci(0x1,0x1)/Ata(0x0)
+Press ESC in 4 seconds to skip startup.nsh or any other key to continue.
+Shell> fs0:
+FS0:\> SimplestApp.efi
+FS0:\>
+```