From: Josef Bacik <josef@xxxxxxxxxxxxxx> FS_PRE_ACCESS will be generated on page fault depending on the faulting method. This pre-content event is meant to be used by hierarchical storage managers that want to fill in the file content on first read access. Export a simple helper that file systems that have their own ->fault() will use, and have a more complicated helper to be do fancy things in filemap_fault. Signed-off-by: Josef Bacik <josef@xxxxxxxxxxxxxx> Signed-off-by: Jan Kara <jack@xxxxxxx> Link: https://patch.msgid.link/aa56c50ce81b1fd18d7f5d71dd2dfced5eba9687.1731684329.git.josef@xxxxxxxxxxxxxx --- include/linux/mm.h | 1 + mm/filemap.c | 78 ++++++++++++++++++++++++++++++++++++++++++++++ mm/nommu.c | 7 +++++ 3 files changed, 86 insertions(+) diff --git a/include/linux/mm.h b/include/linux/mm.h index ecf63d2b0582..e9077ab16972 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -3405,6 +3405,7 @@ extern vm_fault_t filemap_fault(struct vm_fault *vmf); extern vm_fault_t filemap_map_pages(struct vm_fault *vmf, pgoff_t start_pgoff, pgoff_t end_pgoff); extern vm_fault_t filemap_page_mkwrite(struct vm_fault *vmf); +extern vm_fault_t filemap_fsnotify_fault(struct vm_fault *vmf); extern unsigned long stack_guard_gap; /* Generic expand stack which grows the stack according to GROWS{UP,DOWN} */ diff --git a/mm/filemap.c b/mm/filemap.c index 98f15dccff89..0648bb568259 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -47,6 +47,7 @@ #include <linux/splice.h> #include <linux/rcupdate_wait.h> #include <linux/sched/mm.h> +#include <linux/fsnotify.h> #include <asm/pgalloc.h> #include <asm/tlbflush.h> #include "internal.h" @@ -3287,6 +3288,52 @@ static vm_fault_t filemap_fault_recheck_pte_none(struct vm_fault *vmf) return ret; } +/** + * filemap_fsnotify_fault - maybe emit a pre-content event. + * @vmf: struct vm_fault containing details of the fault. + * @folio: the folio we're faulting in. + * + * If we have a pre-content watch on this file we will emit an event for this + * range. If we return anything the fault caller should return immediately, we + * will return VM_FAULT_RETRY if we had to emit an event, which will trigger the + * fault again and then the fault handler will run the second time through. + * + * This is meant to be called with the folio that we will be filling in to make + * sure the event is emitted for the correct range. + * + * Return: a bitwise-OR of %VM_FAULT_ codes, 0 if nothing happened. + */ +vm_fault_t filemap_fsnotify_fault(struct vm_fault *vmf) +{ + struct file *fpin = NULL; + int mask = (vmf->flags & FAULT_FLAG_WRITE) ? MAY_WRITE : MAY_ACCESS; + loff_t pos = vmf->pgoff >> PAGE_SHIFT; + size_t count = PAGE_SIZE; + vm_fault_t ret; + + /* + * We already did this and now we're retrying with everything locked, + * don't emit the event and continue. + */ + if (vmf->flags & FAULT_FLAG_TRIED) + return 0; + + /* No watches, we're done. */ + if (likely(!FMODE_FSNOTIFY_HSM(vmf->vma->vm_file->f_mode))) + return 0; + + fpin = maybe_unlock_mmap_for_io(vmf, fpin); + if (!fpin) + return VM_FAULT_SIGBUS; + + ret = fsnotify_file_area_perm(fpin, mask, &pos, count); + fput(fpin); + if (ret) + return VM_FAULT_SIGBUS; + return VM_FAULT_RETRY; +} +EXPORT_SYMBOL_GPL(filemap_fsnotify_fault); + /** * filemap_fault - read in file data for page fault handling * @vmf: struct vm_fault containing details of the fault @@ -3390,6 +3437,37 @@ vm_fault_t filemap_fault(struct vm_fault *vmf) * or because readahead was otherwise unable to retrieve it. */ if (unlikely(!folio_test_uptodate(folio))) { + /* + * If this is a precontent file we have can now emit an event to + * try and populate the folio. + */ + if (!(vmf->flags & FAULT_FLAG_TRIED) && + unlikely(FMODE_FSNOTIFY_HSM(file->f_mode))) { + loff_t pos = folio_pos(folio); + size_t count = folio_size(folio); + + /* We're NOWAIT, we have to retry. */ + if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT) { + folio_unlock(folio); + goto out_retry; + } + + if (mapping_locked) + filemap_invalidate_unlock_shared(mapping); + mapping_locked = false; + + folio_unlock(folio); + fpin = maybe_unlock_mmap_for_io(vmf, fpin); + if (!fpin) + goto out_retry; + + error = fsnotify_file_area_perm(fpin, MAY_ACCESS, &pos, + count); + if (error) + ret = VM_FAULT_SIGBUS; + goto out_retry; + } + /* * If the invalidate lock is not held, the folio was in cache * and uptodate and now it is not. Strange but possible since we diff --git a/mm/nommu.c b/mm/nommu.c index 385b0c15add8..a8789faa49ee 100644 --- a/mm/nommu.c +++ b/mm/nommu.c @@ -1614,6 +1614,13 @@ int remap_vmalloc_range(struct vm_area_struct *vma, void *addr, } EXPORT_SYMBOL(remap_vmalloc_range); +vm_fault_t filemap_fsnotify_fault(struct vm_fault *vmf) +{ + BUG(); + return 0; +} +EXPORT_SYMBOL_GPL(filemap_fsnotify_fault); + vm_fault_t filemap_fault(struct vm_fault *vmf) { BUG(); -- 2.35.3
