fs: fat: refactor write interface for a file offset

The current write implementation is quite simple: remove existing clusters
and then allocating new ones and filling them with data. This, inevitably,
enforces always writing from the beginning of a file.

As the first step to lift this restriction, fat_file_write() and
set_contents() are modified to accept an additional parameter, file offset
and further re-factored so that, in the next patch, all the necessary code
will be put into set_contents().

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Signed-off-by: Alexander Graf <agraf@suse.de>

diff --git a/fs/fat/fat_write.c b/fs/fat/fat_write.c
index 37ef0564eb5ebc87fe2324962b9f8a37780b52a8..c22d8c7a46a12c4b0b644d3a32f60ae650569c16 100644 (file)
--- a/fs/fat/fat_write.c
+++ b/fs/fat/fat_write.c
@@ -528,6 +528,42 @@ static int clear_fatent(fsdata *mydata, __u32 entry)
        return 0;
 }
 
+/*
+ * Set start cluster in directory entry
+ */
+static void set_start_cluster(const fsdata *mydata, dir_entry *dentptr,
+                             __u32 start_cluster)
+{
+       if (mydata->fatsize == 32)
+               dentptr->starthi =
+                       cpu_to_le16((start_cluster & 0xffff0000) >> 16);
+       dentptr->start = cpu_to_le16(start_cluster & 0xffff);
+}
+
+/*
+ * Check whether adding a file makes the file system to
+ * exceed the size of the block device
+ * Return -1 when overflow occurs, otherwise return 0
+ */
+static int check_overflow(fsdata *mydata, __u32 clustnum, loff_t size)
+{
+       __u32 startsect, sect_num, offset;
+
+       if (clustnum > 0)
+               startsect = clust_to_sect(mydata, clustnum);
+       else
+               startsect = mydata->rootdir_sect;
+
+       sect_num = div_u64_rem(size, mydata->sect_size, &offset);
+
+       if (offset != 0)
+               sect_num++;
+
+       if (startsect + sect_num > total_sector)
+               return -1;
+       return 0;
+}
+
 /*
  * Write at most 'maxsize' bytes from 'buffer' into
  * the file associated with 'dentptr'
@@ -535,29 +571,36 @@ static int clear_fatent(fsdata *mydata, __u32 entry)
  * or return -1 on fatal errors.
  */
 static int
-set_contents(fsdata *mydata, dir_entry *dentptr, __u8 *buffer,
-             loff_t maxsize, loff_t *gotsize)
+set_contents(fsdata *mydata, dir_entry *dentptr, loff_t pos, __u8 *buffer,
+            loff_t maxsize, loff_t *gotsize)
 {
-       loff_t filesize = FAT2CPU32(dentptr->size);
+       loff_t filesize;
        unsigned int bytesperclust = mydata->clust_size * mydata->sect_size;
        __u32 curclust = START(dentptr);
        __u32 endclust = 0, newclust = 0;
        loff_t actsize;
 
        *gotsize = 0;
-       debug("Filesize: %llu bytes\n", filesize);
-
-       if (maxsize > 0 && filesize > maxsize)
-               filesize = maxsize;
+       filesize = maxsize;
 
        debug("%llu bytes\n", filesize);
 
-       if (!curclust) {
-               if (filesize) {
-                       debug("error: nonempty clusterless file!\n");
+       if (curclust) {
+               /*
+                * release already-allocated clusters anyway
+                */
+               if (clear_fatent(mydata, curclust)) {
+                       printf("Error: clearing FAT entries\n");
                        return -1;
                }
-               return 0;
+       }
+
+       curclust = find_empty_cluster(mydata);
+       set_start_cluster(mydata, dentptr, curclust);
+
+       if (check_overflow(mydata, curclust, filesize)) {
+               printf("Error: no space left: %llu\n", filesize);
+               return -1;
        }
 
        actsize = bytesperclust;
@@ -568,6 +611,7 @@ set_contents(fsdata *mydata, dir_entry *dentptr, __u8 *buffer,
                        newclust = determine_fatent(mydata, endclust);
 
                        if ((newclust - 1) != endclust)
+                               /* write to <curclust..endclust> */
                                goto getit;
 
                        if (CHECK_CLUST(newclust, mydata->fatsize)) {
@@ -614,18 +658,8 @@ getit:
                actsize = bytesperclust;
                curclust = endclust = newclust;
        } while (1);
-}
 
-/*
- * Set start cluster in directory entry
- */
-static void set_start_cluster(const fsdata *mydata, dir_entry *dentptr,
-                               __u32 start_cluster)
-{
-       if (mydata->fatsize == 32)
-               dentptr->starthi =
-                       cpu_to_le16((start_cluster & 0xffff0000) >> 16);
-       dentptr->start = cpu_to_le16(start_cluster & 0xffff);
+       return 0;
 }
 
 /*
@@ -642,31 +676,6 @@ static void fill_dentry(fsdata *mydata, dir_entry *dentptr,
        set_name(dentptr, filename);
 }
 
-/*
- * Check whether adding a file makes the file system to
- * exceed the size of the block device
- * Return -1 when overflow occurs, otherwise return 0
- */
-static int check_overflow(fsdata *mydata, __u32 clustnum, loff_t size)
-{
-       __u32 startsect, sect_num, offset;
-
-       if (clustnum > 0) {
-               startsect = clust_to_sect(mydata, clustnum);
-       } else {
-               startsect = mydata->rootdir_sect;
-       }
-
-       sect_num = div_u64_rem(size, mydata->sect_size, &offset);
-
-       if (offset != 0)
-               sect_num++;
-
-       if (startsect + sect_num > total_sector)
-               return -1;
-       return 0;
-}
-
 /*
  * Find a directory entry based on filename or start cluster number
  * If the directory entry is not found,
@@ -784,11 +793,10 @@ static int normalize_longname(char *l_filename, const char *filename)
        return 0;
 }
 
-static int do_fat_write(const char *filename, void *buffer, loff_t size,
-                       loff_t *actwrite)
+int file_fat_write_at(const char *filename, loff_t pos, void *buffer,
+                     loff_t size, loff_t *actwrite)
 {
        dir_entry *retdent;
-       __u32 start_cluster;
        fsdata datablock = { .fatbuf = NULL, };
        fsdata *mydata = &datablock;
        fat_itr *itr = NULL;
@@ -796,6 +804,8 @@ static int do_fat_write(const char *filename, void *buffer, loff_t size,
        char *filename_copy, *parent, *basename;
        char l_filename[VFAT_MAXLEN_BYTES];
 
+       debug("writing %s\n", filename);
+
        filename_copy = strdup(filename);
        if (!filename_copy)
                return -ENOMEM;
@@ -839,47 +849,8 @@ static int do_fat_write(const char *filename, void *buffer, loff_t size,
                        goto exit;
                }
 
-               /* Update file size and start_cluster in a directory entry */
-               retdent->size = cpu_to_le32(size);
-               start_cluster = START(retdent);
-
-               if (start_cluster) {
-                       if (size) {
-                               ret = check_overflow(mydata, start_cluster,
-                                                       size);
-                               if (ret) {
-                                       printf("Error: %llu overflow\n", size);
-                                       ret = -ENOSPC;
-                                       goto exit;
-                               }
-                       }
-
-                       ret = clear_fatent(mydata, start_cluster);
-                       if (ret) {
-                               printf("Error: clearing FAT entries\n");
-                               ret = -EIO;
-                               goto exit;
-                       }
-
-                       if (!size)
-                               set_start_cluster(mydata, retdent, 0);
-               } else if (size) {
-                       ret = start_cluster = find_empty_cluster(mydata);
-                       if (ret < 0) {
-                               printf("Error: finding empty cluster\n");
-                               ret = -ENOSPC;
-                               goto exit;
-                       }
-
-                       ret = check_overflow(mydata, start_cluster, size);
-                       if (ret) {
-                               printf("Error: %llu overflow\n", size);
-                               ret = -ENOSPC;
-                               goto exit;
-                       }
-
-                       set_start_cluster(mydata, retdent, start_cluster);
-               }
+               /* Update file size in a directory entry */
+               retdent->size = cpu_to_le32(pos + size);
        } else {
                /* Create a new file */
 
@@ -907,32 +878,13 @@ static int do_fat_write(const char *filename, void *buffer, loff_t size,
                        goto exit;
                }
 
-               if (size) {
-                       ret = start_cluster = find_empty_cluster(mydata);
-                       if (ret < 0) {
-                               printf("Error: finding empty cluster\n");
-                               ret = -ENOSPC;
-                               goto exit;
-                       }
-
-                       ret = check_overflow(mydata, start_cluster, size);
-                       if (ret) {
-                               printf("Error: %llu overflow\n", size);
-                               ret = -ENOSPC;
-                               goto exit;
-                       }
-               } else {
-                       start_cluster = 0;
-               }
-
                /* Set attribute as archive for regular file */
-               fill_dentry(itr->fsdata, itr->dent, filename,
-                           start_cluster, size, 0x20);
+               fill_dentry(itr->fsdata, itr->dent, filename, 0, size, 0x20);
 
                retdent = itr->dent;
        }
 
-       ret = set_contents(mydata, retdent, buffer, size, actwrite);
+       ret = set_contents(mydata, retdent, pos, buffer, size, actwrite);
        if (ret < 0) {
                printf("Error: writing contents\n");
                ret = -EIO;
@@ -971,6 +923,5 @@ int file_fat_write(const char *filename, void *buffer, loff_t offset,
                return -EINVAL;
        }
 
-       printf("writing %s\n", filename);
-       return do_fat_write(filename, buffer, maxsize, actwrite);
+       return file_fat_write_at(filename, offset, buffer, maxsize, actwrite);
 }