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Subject[PATCH v4 1/10] fs: Add new flag(FALLOC_FL_COLLAPSE_RANGE) for fallocate
Date
From: Namjae Jeon <namjae.jeon@samsung.com>

Add new flag(FALLOC_FL_COLLAPSE_RANGE) for fallocate.
updated detailed semantics in comments.

Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
Signed-off-by: Ashish Sangwan <a.sangwan@samsung.com>
---
fs/open.c | 24 +++++++++++++++++++++---
include/uapi/linux/falloc.h | 21 +++++++++++++++++++++
2 files changed, 42 insertions(+), 3 deletions(-)

diff --git a/fs/open.c b/fs/open.c
index 4b3e1ed..4a923a5 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -231,7 +231,8 @@ int do_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
return -EINVAL;

/* Return error if mode is not supported */
- if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE))
+ if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE |
+ FALLOC_FL_COLLAPSE_RANGE))
return -EOPNOTSUPP;

/* Punch hole must have keep size set */
@@ -239,11 +240,20 @@ int do_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
!(mode & FALLOC_FL_KEEP_SIZE))
return -EOPNOTSUPP;

+ /* Collapse range should only be used exclusively. */
+ if ((mode & FALLOC_FL_COLLAPSE_RANGE) &&
+ (mode & ~FALLOC_FL_COLLAPSE_RANGE))
+ return -EINVAL;
+
if (!(file->f_mode & FMODE_WRITE))
return -EBADF;

- /* It's not possible punch hole on append only file */
- if (mode & FALLOC_FL_PUNCH_HOLE && IS_APPEND(inode))
+ /*
+ * It's not possible to punch hole or perform collapse range
+ * on append only file
+ */
+ if (mode & (FALLOC_FL_PUNCH_HOLE | FALLOC_FL_COLLAPSE_RANGE)
+ && IS_APPEND(inode))
return -EPERM;

if (IS_IMMUTABLE(inode))
@@ -271,6 +281,14 @@ int do_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
if (((offset + len) > inode->i_sb->s_maxbytes) || ((offset + len) < 0))
return -EFBIG;

+ /*
+ * There is no need to overlap collapse range with EOF, in which case
+ * it is effectively a truncate operation
+ */
+ if ((mode & FALLOC_FL_COLLAPSE_RANGE) &&
+ (offset + len >= i_size_read(inode)))
+ return -EINVAL;
+
if (!file->f_op->fallocate)
return -EOPNOTSUPP;

diff --git a/include/uapi/linux/falloc.h b/include/uapi/linux/falloc.h
index 990c4cc..5b214cc 100644
--- a/include/uapi/linux/falloc.h
+++ b/include/uapi/linux/falloc.h
@@ -5,5 +5,26 @@
#define FALLOC_FL_PUNCH_HOLE 0x02 /* de-allocates range */
#define FALLOC_FL_NO_HIDE_STALE 0x04 /* reserved codepoint */

+/*
+ * FALLOC_FL_COLLAPSE_RANGE is used to remove a range of a file
+ * without leaving a hole in the file. The contents of the file beyond
+ * the range being removed is appended to the start offset of the range
+ * being removed (i.e. the hole that was punched is "collapsed"),
+ * resulting in a file layout that looks like the range that was
+ * removed never existed. As such collapsing a range of a file changes
+ * the size of the file, reducing it by the same length of the range
+ * that has been removed by the operation.
+ *
+ * Different filesystems may implement different limitations on the
+ * granularity of the operation. Most will limit operations to
+ * filesystem block size boundaries, but this boundary may be larger or
+ * smaller depending on the filesystem and/or the configuration of the
+ * filesystem or file.
+ *
+ * Attempting to collapse a range that crosses the end of the file is
+ * considered an illegal operation - just use ftruncate(2) if you need
+ * to collapse a range that crosses EOF.
+ */
+#define FALLOC_FL_COLLAPSE_RANGE 0x08

#endif /* _UAPI_FALLOC_H_ */
--
1.7.9.5


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