[PATCH] btrfs: resize: Allow user to shrink missing device

[Qu Wenruo <wqu@suse.com>]

One user reported an use case where one device can't be replaced due to
tiny device size difference.

Since it's a RAID10 fs, if we go regular "remove missing" it can take a
long time and even not be possible due to lack of space.

So here we work around this situation by allowing user to shrink missing
device.
Then user can go shrink the device first, then replace it.

Reported-by: Nathan Dehnel <ncdehnel@gmail.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/ioctl.c | 29 +++++++++++++++++++++++++----
 1 file changed, 25 insertions(+), 4 deletions(-)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index de730e56d3f5..ebd2f40aca6f 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -1604,6 +1604,7 @@ static noinline int btrfs_ioctl_resize(struct file *file,
 	char *sizestr;
 	char *retptr;
 	char *devstr = NULL;
+	bool missing;
 	int ret = 0;
 	int mod = 0;
 
@@ -1651,7 +1652,10 @@ static noinline int btrfs_ioctl_resize(struct file *file,
 		goto out_free;
 	}
 
-	if (!test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state)) {
+
+	missing = test_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state);
+	if (!test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state) &&
+	    !missing) {
 		btrfs_info(fs_info,
 			   "resizer unable to apply on readonly device %llu",
 		       devid);
@@ -1659,13 +1663,24 @@ static noinline int btrfs_ioctl_resize(struct file *file,
 		goto out_free;
 	}
 
-	if (!strcmp(sizestr, "max"))
+	if (!strcmp(sizestr, "max")) {
+		if (missing) {
+			btrfs_info(fs_info,
+				"'max' can't be used for missing device %llu",
+				   devid);
+			ret = -EPERM;
+			goto out_free;
+		}
 		new_size = device->bdev->bd_inode->i_size;
-	else {
+	} else {
 		if (sizestr[0] == '-') {
 			mod = -1;
 			sizestr++;
 		} else if (sizestr[0] == '+') {
+			if (missing)
+				btrfs_info(fs_info,
+				"'+size' can't be used for missing device %llu",
+					   devid);
 			mod = 1;
 			sizestr++;
 		}
@@ -1694,6 +1709,12 @@ static noinline int btrfs_ioctl_resize(struct file *file,
 			ret = -ERANGE;
 			goto out_free;
 		}
+		if (missing) {
+			ret = -EINVAL;
+			btrfs_info(fs_info,
+			"can not increase device size for missing device %llu",
+				   devid);
+		}
 		new_size = old_size + new_size;
 	}
 
@@ -1701,7 +1722,7 @@ static noinline int btrfs_ioctl_resize(struct file *file,
 		ret = -EINVAL;
 		goto out_free;
 	}
-	if (new_size > device->bdev->bd_inode->i_size) {
+	if (!missing && new_size > device->bdev->bd_inode->i_size) {
 		ret = -EFBIG;
 		goto out_free;
 	}
-- 
2.24.0