123 lines
3.7 KiB
Diff
123 lines
3.7 KiB
Diff
From cf35037d52c2abf383fc3e8db00283a58ffc53db Mon Sep 17 00:00:00 2001
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From: "Richard W.M. Jones" <rjones@redhat.com>
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Date: Thu, 1 May 2025 10:36:23 +0100
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Subject: [PATCH] file: zero: Use BLKDISCARD method if may_trim is set
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If we're allowed to trim and we're writing to a block device,
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previously we hit the case fallocate(FALLOC_FL_ZERO_RANGE) first.
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This succeeds in Linux, zeroing (not trimming) the range.
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However it would be better to trim in this case. Linux supports
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ioctl(BLKDISCARD) on block devices, so try this method first.
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Fixes: https://issues.redhat.com/browse/RHEL-89353
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Reported-by: Germano Veit Michel
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Thanks: Eric Blake
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(cherry picked from commit 7a9ecda24906c64d9f8c7238a96cb3f686e894eb)
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---
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plugins/file/file.c | 50 +++++++++++++++++++++++++++++
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plugins/file/nbdkit-file-plugin.pod | 5 +++
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2 files changed, 55 insertions(+)
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diff --git a/plugins/file/file.c b/plugins/file/file.c
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index d7405f36..dc100bb3 100644
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--- a/plugins/file/file.c
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+++ b/plugins/file/file.c
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@@ -404,6 +404,9 @@ file_dump_plugin (void)
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#ifdef BLKSSZGET
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printf ("file_blksszget=yes\n");
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#endif
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+#ifdef BLKDISCARD
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+ printf ("file_blkdiscard=yes\n");
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+#endif
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#ifdef BLKZEROOUT
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printf ("file_blkzeroout=yes\n");
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#endif
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@@ -506,6 +509,7 @@ struct handle {
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bool can_punch_hole;
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bool can_zero_range;
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bool can_fallocate;
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+ bool can_blkdiscard;
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bool can_blkzeroout;
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};
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@@ -747,6 +751,7 @@ file_open (int readonly)
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h->can_fallocate = true;
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h->can_blkzeroout = h->is_block_device;
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+ h->can_blkdiscard = h->is_block_device;
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return h;
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}
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@@ -1009,6 +1014,51 @@ file_zero (void *handle, uint32_t count, uint64_t offset, uint32_t flags)
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}
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#endif
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+#if defined(BLKDISCARD) && defined(FALLOC_FL_ZERO_RANGE)
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+ /* For aligned range and block device, we can use BLKDISCARD to
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+ * trim. However BLKDISCARD doesn't necessarily zero (eg for local
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+ * disk) so we have to zero first and then discard.
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+ *
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+ * In future all Linux block devices may understand
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+ * FALLOC_FL_PUNCH_HOLE which means this case would no longer be
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+ * necessary, since the case above will handle it.
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+ */
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+ if (may_trim && h->can_blkdiscard && h->can_zero_range &&
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+ IS_ALIGNED (offset | count, h->sector_size)) {
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+ int r;
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+ uint64_t range[2] = {offset, count};
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+
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+ r = do_fallocate (h->fd, FALLOC_FL_ZERO_RANGE, offset, count);
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+ if (r == 0) {
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+ /* We could use FALLOC_FL_PUNCH_HOLE here instead, but currently
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+ * thin LVs do not support it (XXX 2025-04).
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+ */
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+ r = ioctl (h->fd, BLKDISCARD, &range);
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+ if (r == 0) {
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+ if (file_debug_zero)
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+ nbdkit_debug ("h->can_blkdiscard && may_trim && IS_ALIGNED: "
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+ "zero succeeded using BLKDISCARD");
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+ goto out;
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+ }
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+
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+ if (!is_enotsup (errno)) {
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+ nbdkit_error ("zero: %m");
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+ return -1;
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+ }
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+
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+ h->can_blkdiscard = false;
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+ }
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+ else {
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+ if (!is_enotsup (errno)) {
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+ nbdkit_error ("zero: %m");
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+ return -1;
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+ }
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+
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+ h->can_fallocate = false;
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+ }
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+ }
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+#endif
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+
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#ifdef FALLOC_FL_ZERO_RANGE
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if (h->can_zero_range) {
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int r;
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diff --git a/plugins/file/nbdkit-file-plugin.pod b/plugins/file/nbdkit-file-plugin.pod
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index 43fc23c7..f1b33582 100644
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--- a/plugins/file/nbdkit-file-plugin.pod
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+++ b/plugins/file/nbdkit-file-plugin.pod
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@@ -237,6 +237,11 @@ block devices.
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If both set, the plugin may be able to efficiently zero ranges of
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block devices, where the driver and block device itself supports this.
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+=item C<file_blkdiscard=yes>
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+
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+If set, the plugin may be able to efficiently trim ranges of block
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+devices, where the driver and block device itself supports this.
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+
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=item C<file_extents=yes>
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If set, the plugin can read file extents.
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--
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2.47.1
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