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fs: sort out the fallocate mode vs flag mess

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The fallocate system call takes a mode argument, but that argument
contains a wild mix of exclusive modes and an optional flags.

Replace FALLOC_FL_SUPPORTED_MASK with FALLOC_FL_MODE_MASK, which excludes
the optional flag bit, so that we can use switch statement on the value
to easily enumerate the cases while getting the check for duplicate modes
for free.

To make this (and in the future the file system implementations) more
readable also add a symbolic name for the 0 mode used to allocate blocks.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20240827065123.1762168-4-hch@lst.de
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Christoph Hellwig 2024-08-27 08:50:47 +02:00 committed by Christian Brauner
parent f951171044
commit 57413d8e17
3 changed files with 38 additions and 32 deletions
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49
fs/open.c
View File

@ -252,40 +252,39 @@ int vfs_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
if (offset < 0 || len <= 0)
return -EINVAL;
/* Return error if mode is not supported */
if (mode & ~FALLOC_FL_SUPPORTED_MASK)
if (mode & ~(FALLOC_FL_MODE_MASK | FALLOC_FL_KEEP_SIZE))
return -EOPNOTSUPP;
/* Punch hole and zero range are mutually exclusive */
if ((mode & (FALLOC_FL_PUNCH_HOLE | FALLOC_FL_ZERO_RANGE)) ==
(FALLOC_FL_PUNCH_HOLE | FALLOC_FL_ZERO_RANGE))
/*
* Modes are exclusive, even if that is not obvious from the encoding
* as bit masks and the mix with the flag in the same namespace.
*
* To make things even more complicated, FALLOC_FL_ALLOCATE_RANGE is
* encoded as no bit set.
*/
switch (mode & FALLOC_FL_MODE_MASK) {
case FALLOC_FL_ALLOCATE_RANGE:
case FALLOC_FL_UNSHARE_RANGE:
case FALLOC_FL_ZERO_RANGE:
break;
case FALLOC_FL_PUNCH_HOLE:
if (!(mode & FALLOC_FL_KEEP_SIZE))
return -EOPNOTSUPP;
/* Punch hole must have keep size set */
if ((mode & FALLOC_FL_PUNCH_HOLE) &&
!(mode & FALLOC_FL_KEEP_SIZE))
break;
case FALLOC_FL_COLLAPSE_RANGE:
case FALLOC_FL_INSERT_RANGE:
if (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;
/* Insert range should only be used exclusively. */
if ((mode & FALLOC_FL_INSERT_RANGE) &&
(mode & ~FALLOC_FL_INSERT_RANGE))
return -EINVAL;
/* Unshare range should only be used with allocate mode. */
if ((mode & FALLOC_FL_UNSHARE_RANGE) &&
(mode & ~(FALLOC_FL_UNSHARE_RANGE | FALLOC_FL_KEEP_SIZE)))
return -EINVAL;
break;
default:
return -EOPNOTSUPP;
}
if (!(file->f_mode & FMODE_WRITE))
return -EBADF;
/*
* We can only allow pure fallocate on append only files
* On append-only files only space preallocation is supported.
*/
if ((mode & ~FALLOC_FL_KEEP_SIZE) && IS_APPEND(inode))
return -EPERM;

8
include/linux/falloc.h
View File

@ -25,7 +25,13 @@ struct space_resv {
#define FS_IOC_UNRESVSP64 _IOW('X', 43, struct space_resv)
#define FS_IOC_ZERO_RANGE _IOW('X', 57, struct space_resv)
#define FALLOC_FL_SUPPORTED_MASK (FALLOC_FL_KEEP_SIZE | \
/*
* Mask of all supported fallocate modes. Only one can be set at a time.
*
* In addition to the mode bit, the mode argument can also encode flags.
* FALLOC_FL_KEEP_SIZE is the only supported flag so far.
*/
#define FALLOC_FL_MODE_MASK (FALLOC_FL_ALLOCATE_RANGE | \
FALLOC_FL_PUNCH_HOLE | \
FALLOC_FL_COLLAPSE_RANGE | \
FALLOC_FL_ZERO_RANGE | \

1
include/uapi/linux/falloc.h
View File

@ -2,6 +2,7 @@
#ifndef _UAPI_FALLOC_H_
#define _UAPI_FALLOC_H_
#define FALLOC_FL_ALLOCATE_RANGE 0x00 /* allocate range */
#define FALLOC_FL_KEEP_SIZE 0x01 /* default is extend size */
#define FALLOC_FL_PUNCH_HOLE 0x02 /* de-allocates range */
#define FALLOC_FL_NO_HIDE_STALE 0x04 /* reserved codepoint */