[PATCH v2 1/2] Add __do_ftruncate that truncates a struct file*

Tony Solomonik
2024-01-23T11:33:38Z

do_sys_ftruncate receives a file descriptor, fgets the struct file*, and
finally actually truncates the file.

__do_ftruncate allows for truncating a file without fgets.
---
fs/open.c | 52 ++++++++++++++++++++++++----------------
include/linux/syscalls.h | 2 ++
2 files changed, 33 insertions(+), 21 deletions(-)

diff --git a/fs/open.c b/fs/open.c
index 02dc608d40d8..b32ac430666c 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -154,47 +154,57 @@ COMPAT_SYSCALL_DEFINE2(truncate, const char __user *, path, compat_off_t, length
}
#endif

-long do_sys_ftruncate(unsigned int fd, loff_t length, int small)
+long __do_ftruncate(struct file *file, loff_t length, int small)
{
struct inode *inode;
struct dentry *dentry;
- struct fd f;
int error;

- error = -EINVAL;
- if (length < 0)
- goto out;
- error = -EBADF;
- f = fdget(fd);
- if (!f.file)
- goto out;
-
/* explicitly opened as large or we are on 64-bit box */
- if (f.file->f_flags & O_LARGEFILE)
+ if (file->f_flags & O_LARGEFILE)
small = 0;

- dentry = f.file->f_path.dentry;
+ dentry = file->f_path.dentry;
inode = dentry->d_inode;
error = -EINVAL;
- if (!S_ISREG(inode->i_mode) || !(f.file->f_mode & FMODE_WRITE))
- goto out_putf;
+ if (!S_ISREG(inode->i_mode) || !(file->f_mode & FMODE_WRITE))
+ goto out;

error = -EINVAL;
/* Cannot ftruncate over 2^31 bytes without large file support */
if (small && length > MAX_NON_LFS)
- goto out_putf;
+ goto out;

error = -EPERM;
/* Check IS_APPEND on real upper inode */
- if (IS_APPEND(file_inode(f.file)))
- goto out_putf;
+ if (IS_APPEND(file_inode(file)))
+ goto out;
sb_start_write(inode->i_sb);
- error = security_file_truncate(f.file);
+ error = security_file_truncate(file);
if (!error)
- error = do_truncate(file_mnt_idmap(f.file), dentry, length,
- ATTR_MTIME | ATTR_CTIME, f.file);
+ error = do_truncate(file_mnt_idmap(file), dentry, length,
+ ATTR_MTIME | ATTR_CTIME, file);
sb_end_write(inode->i_sb);
-out_putf:
+
+out:
+ return error;
+}
+
+long do_sys_ftruncate(unsigned int fd, loff_t length, int small)
+{
+ struct fd f;
+ int error;
+
+ error = -EINVAL;
+ if (length < 0)
+ goto out;
+ error = -EBADF;
+ f = fdget(fd);
+ if (!f.file)
+ goto out;
+
+ error = __do_ftruncate(f.file, length, small);
+
fdput(f);
out:
return error;
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index fd9d12de7e92..e8c56986e751 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -1229,6 +1229,8 @@ static inline long ksys_lchown(const char __user *filename, uid_t user,
AT_SYMLINK_NOFOLLOW);
}

+extern long __do_ftruncate(struct file *file, loff_t length, int small);
+
extern long do_sys_ftruncate(unsigned int fd, loff_t length, int small);

static inline long ksys_ftruncate(unsigned int fd, loff_t length)
--
2.34.1