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    Subject[RFC PATCH 4/8] fsdax: copy data before write
    Date
    Add dax_copy_edges() into each dax actor functions to perform CoW.

    Signed-off-by: Shiyang Ruan <ruansy.fnst@cn.fujitsu.com>
    ---
    fs/dax.c | 39 +++++++++++++++++++++++++++++++++++----
    1 file changed, 35 insertions(+), 4 deletions(-)

    diff --git a/fs/dax.c b/fs/dax.c
    index 308678c58d4d..65553e3f7602 100644
    --- a/fs/dax.c
    +++ b/fs/dax.c
    @@ -1208,7 +1208,8 @@ dax_iomap_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
    return iov_iter_zero(min(length, end - pos), iter);
    }

    - if (WARN_ON_ONCE(iomap->type != IOMAP_MAPPED))
    + if (WARN_ON_ONCE(iomap->type != IOMAP_MAPPED &&
    + !(iomap->flags & IOMAP_F_SHARED)))
    return -EIO;

    /*
    @@ -1247,6 +1248,12 @@ dax_iomap_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
    break;
    }

    + if (iomap != srcmap) {
    + ret = dax_copy_edges(pos, length, srcmap, kaddr, false);
    + if (ret)
    + break;
    + }
    +
    map_len = PFN_PHYS(map_len);
    kaddr += offset;
    map_len -= offset;
    @@ -1358,6 +1365,7 @@ static vm_fault_t dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
    vm_fault_t ret = 0;
    void *entry;
    pfn_t pfn;
    + void *kaddr;

    trace_dax_pte_fault(inode, vmf, ret);
    /*
    @@ -1439,19 +1447,27 @@ static vm_fault_t dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,

    switch (iomap.type) {
    case IOMAP_MAPPED:
    +cow:
    if (iomap.flags & IOMAP_F_NEW) {
    count_vm_event(PGMAJFAULT);
    count_memcg_event_mm(vma->vm_mm, PGMAJFAULT);
    major = VM_FAULT_MAJOR;
    }
    error = dax_iomap_direct_access(&iomap, pos, PAGE_SIZE, &pfn,
    - NULL);
    + &kaddr);
    if (error < 0)
    goto error_finish_iomap;

    entry = dax_insert_entry(&xas, mapping, vmf, iomap.addr, entry,
    pfn, 0, write && !sync);

    + if (srcmap.type != IOMAP_HOLE) {
    + error = dax_copy_edges(pos, PAGE_SIZE, &srcmap, kaddr,
    + false);
    + if (error)
    + goto error_finish_iomap;
    + }
    +
    /*
    * If we are doing synchronous page fault and inode needs fsync,
    * we can insert PTE into page tables only after that happens.
    @@ -1475,12 +1491,15 @@ static vm_fault_t dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,

    goto finish_iomap;
    case IOMAP_UNWRITTEN:
    + if (write && iomap.flags & IOMAP_F_SHARED)
    + goto cow;
    + fallthrough;
    case IOMAP_HOLE:
    if (!write) {
    ret = dax_load_hole(&xas, mapping, &entry, vmf);
    goto finish_iomap;
    }
    - /*FALLTHRU*/
    + fallthrough;
    default:
    WARN_ON_ONCE(1);
    error = -EIO;
    @@ -1582,6 +1601,7 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
    loff_t pos;
    int error;
    pfn_t pfn;
    + void *kaddr;

    /*
    * Check whether offset isn't beyond end of file now. Caller is
    @@ -1663,14 +1683,22 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,

    switch (iomap.type) {
    case IOMAP_MAPPED:
    +cow:
    error = dax_iomap_direct_access(&iomap, pos, PMD_SIZE, &pfn,
    - NULL);
    + &kaddr);
    if (error < 0)
    goto finish_iomap;

    entry = dax_insert_entry(&xas, mapping, vmf, iomap.addr, entry,
    pfn, DAX_PMD, write && !sync);

    + if (srcmap.type != IOMAP_HOLE) {
    + error = dax_copy_edges(pos, PMD_SIZE, &srcmap, kaddr,
    + true);
    + if (error)
    + goto unlock_entry;
    + }
    +
    /*
    * If we are doing synchronous page fault and inode needs fsync,
    * we can insert PMD into page tables only after that happens.
    @@ -1689,6 +1717,9 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
    result = vmf_insert_pfn_pmd(vmf, pfn, write);
    break;
    case IOMAP_UNWRITTEN:
    + if (write && iomap.flags & IOMAP_F_SHARED)
    + goto cow;
    + fallthrough;
    case IOMAP_HOLE:
    if (WARN_ON_ONCE(write))
    break;
    --
    2.27.0


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