Hello,
I need some help with extending the VFS for my project. I need hardlink support, so I added the following to repos/os/include/vfs/directory_service.h's Directory_service struct:
virtual int hardlink(char const *path, char const *hardlink_path) { (void) path; (void)hardlink_path; Genode::error("not implemented!"); return 0; }
I have the Lwext4 plugin (https://codeberg.org/jws/genode-wundertuete/src/branch/import-lwext4_from_wo...) setup for my project so I then extended repos/wundertuete/src/lib/vfs/lwext4/vfs.cc's Lwext4_vfs_file_system struct:
int hardlink(char const *path, char const *hardlink_path) override { return ext4_flink(path, hardlink_path); }
The problem is that hardlink uses the default implementation in my main code: squidutils->_vfs_env.root_dir().hardlink(p2.string(), p1.string()); // Prints 'not implemented'
From what I have read online the issue is that squidutils->_vfs_env.root_dir() is of type Directory_service, whereas I need it to be Lwext4_vfs_file_system. However, Lwext4_vfs_file_system is declared in the vfs.cc file above as opposed to being declared in a header.
Is there a way to use Lwext4_vfs_file_system without copying the entire source of Lwext4 into my project's source code? Or am I perhaps going in the wrong direction with all of this?
Best, Rumen
Hi Rumen,
'Patching' Genode to make it support hardlinks, even limiting said support to local
file systems (no <fs/> connection to a vfs server), would probably be involved :
There a stack of different layers involved, you'd probably need to patch each one of them
to 'propagate' the call from top to bottom layer.
The example below does not use LibC but directly calls the Genode API, that's one
less thing to worry about, but there still remains a few layers:
* an FS plug-in is a subclass of Vfs::File_system ; in the below example, you've added a hardlink() method to the subclass, but (like other methods) it should probably be an "override" of a base-class 'abstract' method/hook
* once the Vfs::File_system base class does have the abstract hook, that hook must be called from other layers above it.
If it was me, I might start my deep dive by doing a "grep -r openlink" or "opendir". (openlink() and opendir() are some of the hooks provided by File_system I think, there are others of course but grepping for it should yield a better digest of results than grepping for more generic terms like open/close/directory etc).
Is there no way for you to use sym-links instead ?
Cédric
De : Rumen Mitov Rumen.Mitov@constructor.tech À : users@lists.genode.org users@lists.genode.org Sujet : Extending the VFS with hard-links Date : 02/04/2025 08:00:28 Europe/Paris
Hello,
I need some help with extending the VFS for my project. I need hardlink support, so I added the following to repos/os/include/vfs/directory_service.h's Directory_service struct:
virtual int hardlink(char const *path, char const *hardlink_path)
{
(void) path;
(void)hardlink_path;
Genode::error("not implemented!");
return 0;
}
I have the Lwext4 plugin (https://codeberg.org/jws/genode-wundertuete/src/branch/import-lwext4_from_wo... for my project so I then extended repos/wundertuete/src/lib/vfs/lwext4/vfs.cc's Lwext4_vfs_file_system struct:
int hardlink(char const *path, char const *hardlink_path) override
{
return ext4_flink(path, hardlink_path);
}
The problem is that hardlink uses the default implementation in my main code: squidutils->_vfs_env.root_dir().hardlink(p2.string(), p1.string()); // Prints 'not implemented'
From what I have read online the issue is that squidutils->_vfs_env.root_dir() is of type Directory_service, whereas I need it to be Lwext4_vfs_file_system. However, Lwext4_vfs_file_system is declared in the vfs.cc file above as opposed to being declared in a header.
Is there a way to use Lwext4_vfs_file_system without copying the entire source of Lwext4 into my project's source code? Or am I perhaps going in the wrong direction with all of this?
Best, Rumen _______________________________________________ users mailing list -- users@lists.genode.org To unsubscribe send an email to users-leave@lists.genode.org Archived at https://lists.genode.org/mailman3/hyperkitty/list/users@lists.genode.org/mes...
Hi Rumen,
just a disclaimer, extending the VFS with hardlink support is not something we endorse because of prior experience and the lack of complelling use-cases that balance out the pitfalls.
I need some help with extending the VFS for my project. I need hardlink support, so I added the following to repos/os/include/vfs/directory_service.h's Directory_service struct: […] The problem is that hardlink uses the default implementation in my main code: squidutils->_vfs_env.root_dir().hardlink(p2.string(), p1.string()); // Prints 'not implemented' […] From what I have read online the issue is that squidutils->_vfs_env.root_dir() is of type Directory_service, whereas […]
You have to implement hardlink support in other VFS plugins, namely the 'Dir_file_system' as this is normally the file-system you access via 'root_dir()', as well. Otherwise you are not going to end up in the lwext4 VFS plugin. The implementation of 'openlink' can show you the way.
Is there a way to use Lwext4_vfs_file_system without copying the entire source of Lwext4 into my project's source code? Or am I perhaps going in the wrong direction with all of this?
If you follow the advice given above you should be able to make use of the lwext4 VFS plugin w/o the need to create copy.
In a previous e-mail I advised against using the lwext4 library directly but perhaps iff there is no particular reason to use the VFS it could be more beneficial to go in this direction after all. The by now removed code in [1] illustrates how you can access the Block session w/o relying on the VFS.
[1] https://github.com/genodelabs/genode-world/blob/3b8e174b6a213346ff7ebcbeeb10...
Regards Josef
Thanks for all the help. I managed to compile everything and now I am trying to debug my implementation.
I am currently stuck on getting gdb to attach to the vfs_lwext4 plugin. My assumption is that the entrypoint is vfs_file_system_factor, so I added a wait_for_continue() in there.
However, after I run gdb (via the attached script), my breakpoints are ignored. I have applied the patch for linux-base and breakpoints work when I try debugging my main program.
I later saw that vfs_lwext4_fs has two processes, so I manually running the steps from my gdb script with each pid. Unfortunately, neither of them worked.
I then tried switching threads in gdb but that was also unsuccessful.
Any suggestions on how I can get this to work?
Best, Rumen ________________________________ From: Josef Söntgen josef.soentgen@genode-labs.com Sent: Thursday, April 3, 2025 12:18 PM To: Genode users mailing list users@lists.genode.org Subject: Re: Extending the VFS with hard-links
CAUTION: This email originated from outside the organization. Do not click links or open attachments unless you recognize the sender and know the content is safe.
Hi Rumen,
just a disclaimer, extending the VFS with hardlink support is not something we endorse because of prior experience and the lack of complelling use-cases that balance out the pitfalls.
I need some help with extending the VFS for my project. I need hardlink support, so I added the following to repos/os/include/vfs/directory_service.h's Directory_service struct: […] The problem is that hardlink uses the default implementation in my main code: squidutils->_vfs_env.root_dir().hardlink(p2.string(), p1.string()); // Prints 'not implemented' […] From what I have read online the issue is that squidutils->_vfs_env.root_dir() is of type Directory_service, whereas […]
You have to implement hardlink support in other VFS plugins, namely the 'Dir_file_system' as this is normally the file-system you access via 'root_dir()', as well. Otherwise you are not going to end up in the lwext4 VFS plugin. The implementation of 'openlink' can show you the way.
Is there a way to use Lwext4_vfs_file_system without copying the entire source of Lwext4 into my project's source code? Or am I perhaps going in the wrong direction with all of this?
If you follow the advice given above you should be able to make use of the lwext4 VFS plugin w/o the need to create copy.
In a previous e-mail I advised against using the lwext4 library directly but perhaps iff there is no particular reason to use the VFS it could be more beneficial to go in this direction after all. The by now removed code in [1] illustrates how you can access the Block session w/o relying on the VFS.
[1] https://github.com/genodelabs/genode-world/blob/3b8e174b6a213346ff7ebcbeeb10...
Regards Josef
-- Josef Söntgen Genode Labs
Hi Rumen,
one suggestion would be to change to the debug directory and run 'gdb ./squid -p $port' there. This should automatically load the symbols of all shared libraries except for ld-linux.lib.so, which still needs 'add-symbol-file ld-linux.lib.so' or a symlink named 'ld.lib.so'.
If it still doesn't work the output of gdb might be helpful.
Christian
On 02.05.25 10:05, Rumen Mitov wrote:
Thanks for all the help. I managed to compile everything and now I am trying to debug my implementation.
I am currently stuck on getting gdb to attach to the vfs_lwext4 plugin. My assumption is that the entrypoint is |vfs_file_system_factor|, so I added a wait_for_continue() in there.
However, after I run gdb (via the attached script), my breakpoints are ignored. I have applied the patch for linux-base and breakpoints work when I try debugging my main program.
I later saw that vfs_lwext4_fs has two processes, so I manually running the steps from my gdb script with each pid. Unfortunately, neither of them worked.
I then tried switching threads in gdb but that was also unsuccessful.
Any suggestions on how I can get this to work?
Best, Rumen
*From:* Josef Söntgen josef.soentgen@genode-labs.com *Sent:* Thursday, April 3, 2025 12:18 PM *To:* Genode users mailing list users@lists.genode.org *Subject:* Re: Extending the VFS with hard-links CAUTION: This email originated from outside the organization. Do not click links or open attachments unless you recognize the sender and know the content is safe.
Hi Rumen,
just a disclaimer, extending the VFS with hardlink support is not something we endorse because of prior experience and the lack of complelling use-cases that balance out the pitfalls.
I need some help with extending the VFS for my project. I need hardlink support, so I added the following to repos/os/include/vfs/directory_service.h's Directory_service struct: […] The problem is that hardlink uses the default implementation in my main code: squidutils->_vfs_env.root_dir().hardlink(p2.string(), p1.string()); // Prints 'not implemented' […] From what I have read online the issue is that squidutils->_vfs_env.root_dir() is of type Directory_service, whereas […]
You have to implement hardlink support in other VFS plugins, namely the 'Dir_file_system' as this is normally the file-system you access via 'root_dir()', as well. Otherwise you are not going to end up in the lwext4 VFS plugin. The implementation of 'openlink' can show you the way.
Is there a way to use Lwext4_vfs_file_system without copying the entire source of Lwext4 into my project's source code? Or am I perhaps going in the wrong direction with all of this?
If you follow the advice given above you should be able to make use of the lwext4 VFS plugin w/o the need to create copy.
In a previous e-mail I advised against using the lwext4 library directly but perhaps iff there is no particular reason to use the VFS it could be more beneficial to go in this direction after all. The by now removed code in [1] illustrates how you can access the Block session w/o relying on the VFS.
[1] https://github.com/genodelabs/genode-world/blob/3b8e174b6a213346ff7ebcbeeb10...
Regards Josef
-- Josef Söntgen Genode Labs
http://www.genode-labs.com/%C2%A0%C2%B7 http://genode.org/ http://genode.org/
users mailing list -- users@lists.genode.org To unsubscribe send an email to users-leave@lists.genode.org Archived at https://lists.genode.org/mailman3/hyperkitty/list/users@lists.genode.org/mes...
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