[v3,7/9] erofs: implement .mmap for page cache sharing
Commit Message
In mmap(2), replace vma->vm_file with the anonymous file associated with
the blob, so that the vma will be linked to the address_space of the
blob.
One thing worth noting is that, we return error early in mmap(2) if
users attempt to map beyond the file size. Normally filesystems won't
restrict this in mmap(2). The checking is done in the fault handler,
and SIGBUS will be signaled to users if they actually attempt to access
the area beyond the end of the file. However since vma->vm_file has
been changed to the anonymous file in mmap(2), we can no way derive the
file size of the original file. As file size is immutable in ro
filesystem, let's fail early in mmap(2) in this case.
Signed-off-by: Jingbo Xu <jefflexu@linux.alibaba.com>
---
fs/erofs/fscache.c | 27 +++++++++++++++++++++++++++
1 file changed, 27 insertions(+)
Comments
Hi Jingbo,
Thank you for the patch! Perhaps something to improve:
[auto build test WARNING on xiang-erofs/dev-test]
[also build test WARNING on xiang-erofs/dev xiang-erofs/fixes linus/master v6.2-rc6 next-20230203]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]
url: https://github.com/intel-lab-lkp/linux/commits/Jingbo-Xu/erofs-support-readahead-in-meta-routine/20230203-110255
base: https://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs.git dev-test
patch link: https://lore.kernel.org/r/20230203030143.73105-8-jefflexu%40linux.alibaba.com
patch subject: [PATCH v3 7/9] erofs: implement .mmap for page cache sharing
config: m68k-allyesconfig (https://download.01.org/0day-ci/archive/20230203/202302032301.KaFzWF1g-lkp@intel.com/config)
compiler: m68k-linux-gcc (GCC) 12.1.0
reproduce (this is a W=1 build):
wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
chmod +x ~/bin/make.cross
# https://github.com/intel-lab-lkp/linux/commit/499758ba5c442083b32a76a3fd55b734df0c486b
git remote add linux-review https://github.com/intel-lab-lkp/linux
git fetch --no-tags linux-review Jingbo-Xu/erofs-support-readahead-in-meta-routine/20230203-110255
git checkout 499758ba5c442083b32a76a3fd55b734df0c486b
# save the config file
mkdir build_dir && cp config build_dir/.config
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=m68k olddefconfig
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=m68k SHELL=/bin/bash fs/erofs/
If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <lkp@intel.com>
All warnings (new ones prefixed by >>):
>> fs/erofs/fscache.c:435:12: warning: no previous prototype for 'erofs_fscache_share_fault' [-Wmissing-prototypes]
435 | vm_fault_t erofs_fscache_share_fault(struct vm_fault *vmf)
| ^~~~~~~~~~~~~~~~~~~~~~~~~
vim +/erofs_fscache_share_fault +435 fs/erofs/fscache.c
434
> 435 vm_fault_t erofs_fscache_share_fault(struct vm_fault *vmf)
436 {
437 struct erofs_fscache_finfo *finfo = vmf->vma->vm_file->private_data;
438
439 if (unlikely(vmf->pgoff >= finfo->max_idx))
440 return VM_FAULT_SIGBUS;
441 return filemap_fault(vmf);
442 }
443
@@ -432,9 +432,36 @@ static ssize_t erofs_fscache_share_file_read_iter(struct kiocb *iocb,
return res;
}
+vm_fault_t erofs_fscache_share_fault(struct vm_fault *vmf)
+{
+ struct erofs_fscache_finfo *finfo = vmf->vma->vm_file->private_data;
+
+ if (unlikely(vmf->pgoff >= finfo->max_idx))
+ return VM_FAULT_SIGBUS;
+ return filemap_fault(vmf);
+}
+
+static const struct vm_operations_struct erofs_fscache_share_file_vm_ops = {
+ .fault = erofs_fscache_share_fault,
+};
+
+static int erofs_fscache_share_file_mmap(struct file *file,
+ struct vm_area_struct *vma)
+{
+ struct file *realfile = file->private_data;
+ struct erofs_fscache_finfo *finfo = realfile->private_data;
+
+ vma_set_file(vma, realfile);
+ vma->vm_pgoff = (finfo->pa >> PAGE_SHIFT) + vma->vm_pgoff;
+ vma->vm_ops = &erofs_fscache_share_file_vm_ops;
+ file_accessed(file);
+ return 0;
+}
+
const struct file_operations erofs_fscache_share_file_fops = {
.llseek = generic_file_llseek,
.read_iter = erofs_fscache_share_file_read_iter,
+ .mmap = erofs_fscache_share_file_mmap,
.open = erofs_fscache_share_file_open,
.release = erofs_fscache_share_file_release,
};