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List:       opensuse
Subject:    [opensuse] Re: [opensuse-programming] ext3 - ENOMEM on file write
From:       Roger Oberholtzer <roger () opq ! se>
Date:       2010-04-30 9:58:11
Message-ID: 1272621491.7641.115.camel () acme ! pacific
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On Thu, 2010-04-29 at 18:41 -0600, Cameron Seader wrote:
> Greetings,
> Wondering if anyone here has some experience with this. I have been trying to track \
> this down and have no idea how this is happening. Its not making any sense at all. 
> We have a case where we have a system that is doing some successive reading and \
> writing to a file. 
> Here is the specific Code:
> 
> --snip--
> First, we're given an inode 'ainode', which should be the correct inode
> for the file we're looking at. (If it were incorrect, we would have
> gotten an error much earlier.)
> 
> If we have iget, we call iget. The 2.6.16.60-* kernels lack iget, I
> believe, so instead we do:
> 
> fid.i32.ino = ainode;
> fid.i32.gen = 0;
> dp = afs_cacheSBp->s_export_op->fh_to_dentry(afs_cacheSBp,
> &fid, sizeof(fid), FILEID_INO32_GEN);
> filp = dentry_open(dp, mntget(afs_cacheMnt), O_RDWR);
> 
> (I'm not including error-checking. afs_cacheSBp is the superblock for
> the cache filesystem, so ext2 or ext3. afs_cacheMnt is the vfsmount for
> the cache FS) Then, to write to the file we do basically:
> 
> (we're writing 'count' bytes from 'buf' to 'offset' in file 'filp'; I'm
> paraphrasing the code here, but I think I'm maintaining what it does)
> 
> mm_segment_t _fs_space_decl;
> int code = 0;
> 
> savelim = current->TASK_STRUCT_RLIM[RLIMIT_FSIZE].rlim_cur;
> current->TASK_STRUCT_RLIM[RLIMIT_FSIZE].rlim_cur = RLIM_INFINITY;
> 
> _fs_space_decl = get_fs();
> set_fs(get_ds());
> 
> if (filp->f_op->llseek) {
> if (filp->f_op->llseek(filp, offset, 0) != offset)
> return -1;
> } else {
> filp->f_pos = offset;
> }
> 
> while (code == 0 && count > 0) {
> code = filp->f_op->write(filp, buf, count, &f->f_pos);
> if (code < 0) {
> code = -code;
> break;
> } else if (code == 0) {
> code = EIO;
> break;
> }
> 
> buf += code;
> count -= code;
> code = 0;
> }

If I understand your code, you are not using the return value from
write() properly.

write() returns how many characters were written, or -1 on error. It
never ever contains any error information beyond that. When the return
value does not match 'count', then you must use 'errno' to see what the
problem was. The action to take beyond that depends on if the file
descriptor is blocking or not. For a disk file, and looking at your
sample code, your writes are blocking. So the only two possible return
values from write() are -1 and 'count'. If you get -1. then you should
set code to 'errno'.


-- 
Roger Oberholtzer

OPQ Systems / Ramböll RST

Ramböll Sverige AB
Krukmakargatan 21
P.O. Box 17009
SE-104 62 Stockholm, Sweden

Office: Int +46 10-615 60 20
Mobile: Int +46 70-815 1696

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