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netfs: Allow buffered shared-writeable mmap through netfs_page_mkwrite()

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Provide an entry point to delegate a filesystem's ->page_mkwrite() to.
This checks for conflicting writes, then attached any netfs-specific group
marking (e.g. ceph snap) to the page to be considered dirty.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
This commit is contained in:
David Howells 2022-02-15 23:15:57 +00:00
parent 938e13a73b
commit 102a7e2c59
2 changed files with 63 additions and 0 deletions
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59
fs/netfs/buffered_write.c
View File

@ -416,3 +416,62 @@ ssize_t netfs_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
return ret;
}
EXPORT_SYMBOL(netfs_file_write_iter);
/*
* Notification that a previously read-only page is about to become writable.
* Note that the caller indicates a single page of a multipage folio.
*/
vm_fault_t netfs_page_mkwrite(struct vm_fault *vmf, struct netfs_group *netfs_group)
{
struct folio *folio = page_folio(vmf->page);
struct file *file = vmf->vma->vm_file;
struct inode *inode = file_inode(file);
vm_fault_t ret = VM_FAULT_RETRY;
int err;
_enter("%lx", folio->index);
sb_start_pagefault(inode->i_sb);
if (folio_wait_writeback_killable(folio))
goto out;
if (folio_lock_killable(folio) < 0)
goto out;
/* Can we see a streaming write here? */
if (WARN_ON(!folio_test_uptodate(folio))) {
ret = VM_FAULT_SIGBUS | VM_FAULT_LOCKED;
goto out;
}
if (netfs_folio_group(folio) != netfs_group) {
folio_unlock(folio);
err = filemap_fdatawait_range(inode->i_mapping,
folio_pos(folio),
folio_pos(folio) + folio_size(folio));
switch (err) {
case 0:
ret = VM_FAULT_RETRY;
goto out;
case -ENOMEM:
ret = VM_FAULT_OOM;
goto out;
default:
ret = VM_FAULT_SIGBUS;
goto out;
}
}
if (folio_test_dirty(folio))
trace_netfs_folio(folio, netfs_folio_trace_mkwrite_plus);
else
trace_netfs_folio(folio, netfs_folio_trace_mkwrite);
netfs_set_group(folio, netfs_group);
file_update_time(file);
ret = VM_FAULT_LOCKED;
out:
sb_end_pagefault(inode->i_sb);
return ret;
}
EXPORT_SYMBOL(netfs_page_mkwrite);

4
include/linux/netfs.h
View File

@ -400,6 +400,10 @@ void netfs_clear_inode_writeback(struct inode *inode, const void *aux);
void netfs_invalidate_folio(struct folio *folio, size_t offset, size_t length);
bool netfs_release_folio(struct folio *folio, gfp_t gfp);
/* VMA operations API. */
vm_fault_t netfs_page_mkwrite(struct vm_fault *vmf, struct netfs_group *netfs_group);
/* (Sub)request management API. */
void netfs_subreq_terminated(struct netfs_io_subrequest *, ssize_t, bool);
void netfs_get_subrequest(struct netfs_io_subrequest *subreq,
enum netfs_sreq_ref_trace what);