Re: How to open a file by it's full path in UEFI

["Carsey, Jaben" <jaben.carsey@intel.com>]

Apparently all the good threads happen at night for me...

Kesheva,

There are a few functions in the ShellLib that call into the UEFI Shell binary to help you. Some of these are duplicates of what others suggested, but I figured I would elaborate.

ShellOpenFileMetaArg - open a file or group of files.  can handle something like "open *.txt"
ShellOpenFileByName - open a single file.

These functions in turn call into functions in the ShellProtocol that the UEFI Shell produces during the time it is running.

ShellOpenFileMetaArg  calls into gEfiShellProtocol->OpenFileList
ShellOpenFileByName  calls into gEfiShellProtocol->OpenFileByName

There is some examples of use of these functions in the files for the commands "Touch" and "Type" and these are located in: ShellPkg\Library\UefiShellLevel3CommandsLib


-Jaben

> -----Original Message-----
> From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On Behalf Of
> GN Keshava
> Sent: Tuesday, September 27, 2016 4:52 AM
> To: Laszlo Ersek <lersek@redhat.com>
> Cc: edk2-devel@lists.01.org <edk2-devel@ml01.01.org>
> Subject: Re: [edk2] How to open a file by it's full path in UEFI
> 
> Thank you Laszlo.
> 
> I'll check it out. :)
> 
> Thanks again.
> Regards,
> Keshava
> 
> On Tue, 27 Sep 2016 at 16:47 Laszlo Ersek <lersek@redhat.com> wrote:
> 
> > On 09/27/16 12:46, GN Keshava wrote:
> > > Hi Laszlo,
> > >
> > > Thank you for the answer. It was helpful.
> > >
> > > Considering option #1, can you give some more details (a small example
> > > or any reference link would be helpful), how I can use Shell APIs in my
> > > C file (which will compile to my .efi app)?
> >
> > Hmmm, I don't have hands-on experience with this, but you might want to
> > try the ShellOpenFileByName() function, from
> > "ShellPkg/Include/Library/ShellLib.h".
> >
> > You can find examples for UEFI applications that use the Shell library
> > with:
> >
> >   git grep -w ShellLib -- '*inf'
> >
> > or just grep the tree for ShellOpenFileByName().
> >
> > See also "AppPkg/ReadMe.txt".
> >
> > > Considering option #2, How I can find device path programatically from
> > > my C file?
> >
> > The EFI_SHELL_PROTOCOL.GetDevicePathFromMap() member function
> seems
> > relevant -- it is specified in the UEFI Shell spec --, but I would
> > definitely try ShellOpenFileByName() first.
> >
> > Thanks
> > Laszlo
> >
> > > Thanks again for the help. :)
> > > With regards,
> > > Keshava
> > >
> > > On Tue, 27 Sep 2016 at 15:19 Laszlo Ersek <lersek@redhat.com
> > > <mailto:lersek@redhat.com>> wrote:
> > >
> > >     On 09/27/16 11:25, GN Keshava wrote:
> > >     > Hi Laszlo,
> > >     >
> > >     > Thanks for the reply. I meant I have complete file path. I believe
> > the
> > >     > "device path" is different. Is it possible to obtain DevicePath
> > >     using my
> > >     > full file path?
> > >
> > >     The pathname you seem to have (as "complete") is specific to a given
> > >     simple FS, so system-wide it cannot be considered complete (there
> > can be
> > >     multiple filesystems).
> > >
> > >     In your original email I missed that you started with "FS1:".
> > Andrew's
> > >     answer covers that case.
> > >
> > >     In summary, you can do three things:
> > >     - have a pathname that starts with FSx: (which is a shell-specific
> > >     mapping), and use Andrew's recommendation,
> > >     - have a complete UEFI device path, and then use what I
> recommended,
> > >     - have no information for selecting the filesystem (from the many
> > >     possible), and use your current iteration.
> > >
> > >     Options #1 and #2 actually correspond to each other, considering
> > >     "expressive power" / information content (as long as you are in the
> > >     shell); please see the MAP shell command.
> > >
> > >     Thanks
> > >     Laszlo
> > >
> > >     > On Tue, 27 Sep 2016 at 14:46 Laszlo Ersek <lersek@redhat.com
> > >     <mailto:lersek@redhat.com>
> > >     > <mailto:lersek@redhat.com <mailto:lersek@redhat.com>>> wrote:
> > >     >
> > >     >     On 09/27/16 11:03, GN Keshava wrote:
> > >     >     > Hi all,
> > >     >     >
> > >     >     >
> > >     >     > I'm trying to open a file from my UEFI application. The path
> > of
> > >     >     file is
> > >     >     >
> > >     >     > fs1:/myfolder/myfile.txt
> > >     >     >
> > >     >     > The code :
> > >     >     >
> > >     >     > efiStatus = bs->LocateHandleBuffer(ByProtocol,
> > >     >     >                                    &sfspGuid,
> > >     >     >                                    NULL,
> > >     >     >                                    &handleCount,
> > >     >     >                                    &handles);
> > >     >     >
> > >     >     > for (index = 0; index < (int)handleCount; ++ index)
> > >     >     > {
> > >     >     >     EFI_SIMPLE_FILE_SYSTEM_PROTOCOL* fs = NULL;
> > >     >     >
> > >     >     >     efiStatus = bs->HandleProtocol(
> > >     >     >         handles[index],
> > >     >     >         &sfspGuid,
> > >     >     >         (void**)&fs);
> > >     >     >
> > >     >     >     EFI_FILE_PROTOCOL* root = NULL;
> > >     >     >     ...
> > >     >     >     efiStatus = fs->OpenVolume(fs, &root);
> > >     >     >
> > >     >     >     EFI_FILE_PROTOCOL* token = NULL;
> > >     >     >
> > >     >     >     efiStatus = root->Open(
> > >     >     >         root,
> > >     >     >         &token,
> > >     >     >         L"myfolder\\myfile.txt",
> > >     >     >         EFI_FILE_MODE_READ,
> > >     >     >         EFI_FILE_READ_ONLY | EFI_FILE_HIDDEN |
> > EFI_FILE_SYSTEM);
> > >     >     > }
> > >     >     >
> > >     >     > But using this method, I can only go through all the file
> > system
> > >     >     handles
> > >     >     > and open each volume and try opening my file.
> > >     >     >
> > >     >     > But I want to give full path to my file and open it in it's
> > >     volume.
> > >     >     >
> > >     >     > How can I acheive this?
> > >     >     > Thanks.
> > >     >
> > >     >     If you have a complete device path, you can use
> > >     gBS->LocateDevicePath()
> > >     >     with gEfiSimpleFileSystemProtocolGuid, to locate the handle
> > >     with the
> > >     >     most specific device path (--> the longest device path prefix)
> > >     with the
> > >     >     simple FS protocol installed on it. Then you can check if the
> > >     remaining
> > >     >     device path (returned by the service) consist of nothing but
> > >     one File
> > >     >     Path Media Device Path node. If so, you can open the simple FS
> > >     protocol
> > >     >     on the handle found, then use that to open the file by
> > pathname.
> > >     >
> > >     >     Laszlo
> > >     >
> > >
> >
> >
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