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docs: Cleanup virtio-fs documentation

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Update obsolete information from the virtio-fs documentation.

Fixes #2538

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>
This commit is contained in:
Sebastien Boeuf 2021-04-28 10:37:59 +02:00
parent 3ffc655a38
commit 235eb5225a
1 changed files with 10 additions and 10 deletions
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docs/fs.md
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@ -12,7 +12,7 @@ This virtual device relies on the _vhost-user_ protocol, which assumes the backe
_Build virtiofsd_
```bash
git clone --depth 1 "https://github.com/sboeuf/qemu.git" -b "virtio-fs" $VIRTIOFSD_DIR
git clone --depth 1 "https://gitlab.com/virtio-fs/qemu.git" -b "qemu5.0-virtiofs-dax" $VIRTIOFSD_DIR
cd $VIRTIOFSD_DIR
./configure --prefix=$PWD --target-list=x86_64-softmmu
make virtiofsd -j `nproc`
@ -45,32 +45,32 @@ of older kernels, with additional patches, are not supported.
### Start the VM
Once the daemon is running, the option `--fs` from __cloud-hypervisor__ needs to be used.
Direct kernel boot option is preferred since we need to provide the custom kernel including the __virtio-fs__ patches. We could boot from `hypervisor-fw` if we had previously edited the image to replace the kernel binary.
Direct kernel boot is the preferred option, but we can boot from an EFI cloud image if it contains a recent enough kernel.
Because _vhost-user_ expects a dedicated process (__virtiofsd__ in this case) to be able to access the guest RAM to communicate through the _virtqueues_ with the driver running in the guest, `--memory` option needs to be slightly modified. It needs to specify a backing file for the memory so that an external process can access it.
Because _vhost-user_ expects a dedicated process (__virtiofsd__ in this case) to be able to access the guest RAM to communicate through the _virtqueues_ with the driver running in the guest, `--memory` option needs to be slightly modified. It must specify `shared=on` to share the memory pages so that an external process can access them.
Assuming you have `focal-server-cloudimg-amd64.raw` and `custom-vmlinux.bin` on your system, here is the __cloud-hypervisor__ command you need to run:
Assuming you have `focal-server-cloudimg-amd64.raw` and `vmlinux` on your system, here is the __cloud-hypervisor__ command you need to run:
```bash
./cloud-hypervisor \
--cpus 4 \
--memory "size=512M,shared=on" \
--cpus boot=1 \
--memory size=1G,shared=on \
--disk path=focal-server-cloudimg-amd64.raw \
--kernel custom-vmlinux.bin \
--cmdline "console=ttyS0 console=hvc0 root=/dev/vda1 rw" \
--kernel vmlinux \
--cmdline "console=hvc0 root=/dev/vda1 rw" \
--fs tag=myfs,socket=/tmp/virtiofs,num_queues=1,queue_size=512
```
By default, DAX is enabled with a cache window of 8GiB. You can specify a custom size (let's say 4GiB for this example) for the cache by explicitly setting DAX and the cache size:
```bash
--fs tag=virtiofs,socket=/tmp/virtiofs,num_queues=1,queue_size=512,dax=on,cache_size=4G
--fs tag=myfs,socket=/tmp/virtiofs,num_queues=1,queue_size=512,dax=on,cache_size=4G
```
In case you don't want to use a shared window of cache to pass the shared files content, this means you will have to explicitly disable DAX with `dax=off`. Note that in this case, the `cache_size` parameter will be ignored.
```bash
--fs tag=virtiofs,socket=/tmp/virtiofs,num_queues=1,queue_size=512,dax=off
--fs tag=myfs,socket=/tmp/virtiofs,num_queues=1,queue_size=512,dax=off
```