reproduce:
dd if=/dev/zero of=tmpfile bs=4K count=1
dd if=/dev/zero of=tmpfile1 bs=1M
dd if=/dev/zero of=tmpfile2 bs=4K
rm -f tmpfile
sync
dd if=/dev/zero of=tmpfile bs=8K count=1
We try to create a 8K file when there is only 4K space left, btrfs will write no
data into a file, but under EXT4 it will still write the first 4K data. Also the
POSIX hopes we writting as much as possible.
quote the POSIX:
If a write() requests that more bytes be written than there is room for(for
example,
[XSI] [Option Start] the process'' file size limit or [Option End] the
physical end
of a medium), only as many bytes as there is room for shall be written. For
example,
suppose there is space for 20 bytes more in a file before reaching a limit. A
write
of 512 bytes will return 20. The next write of a non-zero number of bytes would
give
a failure return (except as noted below).
Signed-off-by: Wu Bo <wu.bo@cn.fujitsu.com>
---
fs/btrfs/file.c | 18 ++++++++++++++++--
1 files changed, 16 insertions(+), 2 deletions(-)
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 15e5a1c..b364f05 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1179,11 +1179,14 @@ static noinline ssize_t __btrfs_buffered_write(struct
file *file,
size_t write_bytes = min(iov_iter_count(i),
nrptrs * (size_t)PAGE_CACHE_SIZE -
offset);
- size_t num_pages = (write_bytes + offset +
- PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
+ size_t num_pages;
size_t dirty_pages;
size_t copied;
+again:
+ num_pages = (write_bytes + offset +
+ PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
+
WARN_ON(num_pages > nrptrs);
/*
@@ -1197,6 +1200,17 @@ static noinline ssize_t __btrfs_buffered_write(struct
file *file,
ret = btrfs_delalloc_reserve_space(inode,
num_pages << PAGE_CACHE_SHIFT);
+
+ /* try to reserve smaller space for write */
+ if (ret == -ENOSPC) {
+ if (num_pages > 1) {
+ write_bytes >>= 1;
+ goto again;
+ } else {
+ break;
+ }
+ }
+
if (ret)
break;
--
1.7.3.1
--
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